[RFC patch 16/41] LTTng Transport Locked

From: Mathieu Desnoyers
Date: Thu Mar 05 2009 - 18:36:55 EST

LTTng data relay transport protected by spin lock and interrupt disable.

Performance tests, tbench, flight recorder trace, default instrumentation

Dual quad-core x86_64, 2.0GHz
Instrumentation dynamically disabled : 1883.09 MB/s
Markers connected : 1812.14 MB/s
Lockless scheme, flight recorder : 925.68 MB/s
Per-cpu-buffer spinlock and interrupt disable, flight recorder : 871.78 MB/s
Global spinlock and interrupt disable, flight recorder : 153.74 MB/s

Single Core Pentium 4, noreplace-smp, 3.0GHz
Instrumentation dynamically disabled : 146.85 MB/s
Markers connected : 144.32 MB/s
Lockless scheme, flight recorder : 89.59 MB/s
Per-cpu-buffer spinlock and interrupt disable, flight recorder : 86.05 MB/s


Credits to Lai Jiangshan <laijs@xxxxxxxxxxxxxx> for updates and fixes.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
CC: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
---
ltt/ltt-relay-locked.c | 1704 +++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 1704 insertions(+)

Index: linux-2.6-lttng/ltt/ltt-relay-locked.c
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6-lttng/ltt/ltt-relay-locked.c 2009-03-05 16:33:29.000000000 -0500
@@ -0,0 +1,1704 @@
+/*
+ * ltt/ltt-relay-locked.c
+ *
+ * (C) Copyright 2005-2008 - Mathieu Desnoyers (mathieu.desnoyers@xxxxxxxxxx)
+ *
+ * LTTng buffer space management (reader/writer) using spinlock and interrupt
+ * disable.
+ *
+ * Author:
+ * Mathieu Desnoyers (mathieu.desnoyers@xxxxxxxxxx)
+ *
+ * Inspired from LTT :
+ * Karim Yaghmour (karim@xxxxxxxxxxx)
+ * Tom Zanussi (zanussi@xxxxxxxxxx)
+ * Bob Wisniewski (bob@xxxxxxxxxxxxxx)
+ * And from K42 :
+ * Bob Wisniewski (bob@xxxxxxxxxxxxxx)
+ *
+ * Changelog:
+ * 08/10/08, Fork from lockless mechanism, use spinlock and irqoff.
+ * 19/10/05, Complete lockless mechanism.
+ * 27/05/05, Modular redesign and rewrite.
+ *
+ * Userspace reader semantic :
+ * while (poll fd != POLLHUP) {
+ * - ioctl RELAY_GET_SUBBUF_SIZE
+ * while (1) {
+ * - ioctl GET_SUBBUF
+ * - splice 1 subbuffer worth of data to a pipe
+ * - splice the data from pipe to disk/network
+ * - ioctl PUT_SUBBUF, check error value
+ * if err val < 0, previous subbuffer was corrupted.
+ * }
+ * }
+ */
+
+#include <linux/time.h>
+#include <linux/ltt-tracer.h>
+#include <linux/ltt-relay.h>
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/rcupdate.h>
+#include <linux/sched.h>
+#include <linux/bitops.h>
+#include <linux/fs.h>
+#include <linux/smp_lock.h>
+#include <linux/debugfs.h>
+#include <linux/stat.h>
+#include <linux/cpu.h>
+#include <linux/pipe_fs_i.h>
+#include <linux/splice.h>
+#include <linux/spinlock.h>
+
+#if 0
+#define printk_dbg(fmt, args...) printk(fmt, args)
+#else
+#define printk_dbg(fmt, args...)
+#endif
+
+
+/* LTTng locked logging buffer info */
+struct ltt_channel_buf_struct {
+ /* First 32 bytes cache-hot cacheline */
+ long offset; /* Current offset in the buffer */
+ long *commit_count; /* Commit count per sub-buffer */
+ unsigned long irqflags; /* IRQ flags saved by reserve */
+ raw_spinlock_t lock; /* Spinlock protecting buffer */
+ /* End of first 32 bytes cacheline */
+ unsigned long last_tsc; /*
+ * Last timestamp written in the buffer.
+ */
+ long consumed; /* Current offset in the buffer */
+ atomic_long_t active_readers; /* Active readers count */
+ long events_lost;
+ long corrupted_subbuffers;
+ wait_queue_head_t write_wait; /*
+ * Wait queue for blocking user space
+ * writers
+ */
+ int wakeup_readers; /* Boolean : wakeup readers waiting ? */
+ wait_queue_head_t read_wait; /* reader wait queue */
+ unsigned int finalized; /* buffer has been finalized */
+} ____cacheline_aligned;
+
+static const struct file_operations ltt_file_operations;
+
+/*
+ * Last TSC comparison functions. Check if the current TSC overflows
+ * LTT_TSC_BITS bits from the last TSC read. Reads and writes last_tsc
+ * atomically.
+ */
+
+#if (BITS_PER_LONG == 32)
+static inline void save_last_tsc(struct ltt_channel_buf_struct *ltt_buf,
+ u64 tsc)
+{
+ ltt_buf->last_tsc = (unsigned long)(tsc >> LTT_TSC_BITS);
+}
+
+static inline int last_tsc_overflow(struct ltt_channel_buf_struct *ltt_buf,
+ u64 tsc)
+{
+ unsigned long tsc_shifted = (unsigned long)(tsc >> LTT_TSC_BITS);
+
+ if (unlikely((tsc_shifted - ltt_buf->last_tsc)))
+ return 1;
+ else
+ return 0;
+}
+#else
+static inline void save_last_tsc(struct ltt_channel_buf_struct *ltt_buf,
+ u64 tsc)
+{
+ ltt_buf->last_tsc = (unsigned long)tsc;
+}
+
+static inline int last_tsc_overflow(struct ltt_channel_buf_struct *ltt_buf,
+ u64 tsc)
+{
+ if (unlikely((tsc - ltt_buf->last_tsc) >> LTT_TSC_BITS))
+ return 1;
+ else
+ return 0;
+}
+#endif
+
+/*
+ * A switch is done during tracing or as a final flush after tracing (so it
+ * won't write in the new sub-buffer).
+ */
+enum force_switch_mode { FORCE_ACTIVE, FORCE_FLUSH };
+
+static int ltt_relay_create_buffer(struct ltt_trace_struct *trace,
+ struct ltt_channel_struct *ltt_chan,
+ struct rchan_buf *buf,
+ unsigned int cpu,
+ unsigned int n_subbufs);
+
+static void ltt_relay_destroy_buffer(struct ltt_channel_struct *ltt_chan,
+ unsigned int cpu);
+
+static void ltt_force_switch(struct rchan_buf *buf,
+ enum force_switch_mode mode);
+
+/*
+ * Trace callbacks
+ */
+static void ltt_buffer_begin_callback(struct rchan_buf *buf,
+ u64 tsc, unsigned int subbuf_idx)
+{
+ struct ltt_channel_struct *channel =
+ (struct ltt_channel_struct *)buf->chan->private_data;
+ struct ltt_subbuffer_header *header =
+ (struct ltt_subbuffer_header *)
+ ltt_relay_offset_address(buf,
+ subbuf_idx * buf->chan->subbuf_size);
+
+ header->cycle_count_begin = tsc;
+ header->lost_size = 0xFFFFFFFF; /* for debugging */
+ header->buf_size = buf->chan->subbuf_size;
+ ltt_write_trace_header(channel->trace, header);
+}
+
+/*
+ * offset is assumed to never be 0 here : never deliver a completely empty
+ * subbuffer. The lost size is between 0 and subbuf_size-1.
+ */
+static notrace void ltt_buffer_end_callback(struct rchan_buf *buf,
+ u64 tsc, unsigned int offset, unsigned int subbuf_idx)
+{
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+ struct ltt_subbuffer_header *header =
+ (struct ltt_subbuffer_header *)
+ ltt_relay_offset_address(buf,
+ subbuf_idx * buf->chan->subbuf_size);
+
+ header->lost_size = SUBBUF_OFFSET((buf->chan->subbuf_size - offset),
+ buf->chan);
+ header->cycle_count_end = tsc;
+ header->events_lost = ltt_buf->events_lost;
+ header->subbuf_corrupt = ltt_buf->corrupted_subbuffers;
+}
+
+static notrace void ltt_deliver(struct rchan_buf *buf, unsigned int subbuf_idx,
+ void *subbuf)
+{
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+
+ ltt_buf->wakeup_readers = 1;
+}
+
+static struct dentry *ltt_create_buf_file_callback(const char *filename,
+ struct dentry *parent, int mode,
+ struct rchan_buf *buf)
+{
+ struct ltt_channel_struct *ltt_chan;
+ int err;
+ struct dentry *dentry;
+
+ ltt_chan = buf->chan->private_data;
+ err = ltt_relay_create_buffer(ltt_chan->trace, ltt_chan,
+ buf, buf->cpu,
+ buf->chan->n_subbufs);
+ if (err)
+ return ERR_PTR(err);
+
+ dentry = debugfs_create_file(filename, mode, parent, buf,
+ &ltt_file_operations);
+ if (!dentry)
+ goto error;
+ return dentry;
+error:
+ ltt_relay_destroy_buffer(ltt_chan, buf->cpu);
+ return NULL;
+}
+
+static int ltt_remove_buf_file_callback(struct dentry *dentry)
+{
+ struct rchan_buf *buf = dentry->d_inode->i_private;
+ struct ltt_channel_struct *ltt_chan = buf->chan->private_data;
+
+ debugfs_remove(dentry);
+ ltt_relay_destroy_buffer(ltt_chan, buf->cpu);
+
+ return 0;
+}
+
+/*
+ * Wake writers :
+ *
+ * This must be done after the trace is removed from the RCU list so that there
+ * are no stalled writers.
+ */
+static void ltt_relay_wake_writers(struct ltt_channel_buf_struct *ltt_buf)
+{
+
+ if (waitqueue_active(&ltt_buf->write_wait))
+ wake_up_interruptible(&ltt_buf->write_wait);
+}
+
+/*
+ * This function should not be called from NMI interrupt context
+ */
+static notrace void ltt_buf_unfull(struct rchan_buf *buf,
+ unsigned int subbuf_idx,
+ long offset)
+{
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+
+ ltt_relay_wake_writers(ltt_buf);
+}
+
+/*
+ * Reader API.
+ */
+static unsigned long get_offset(struct rchan_buf *buf)
+{
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+ return ltt_buf->offset;
+}
+
+static unsigned long get_consumed(struct rchan_buf *buf)
+{
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+ return ltt_buf->consumed;
+}
+
+static int _ltt_open(struct rchan_buf *buf)
+{
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+
+ if (!atomic_long_add_unless(&ltt_buf->active_readers, 1, 1))
+ return -EBUSY;
+ ltt_relay_get_chan(buf->chan);
+ return 0;
+}
+
+static int _ltt_release(struct rchan_buf *buf)
+{
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+
+ ltt_relay_put_chan(buf->chan);
+ WARN_ON(atomic_long_read(&ltt_buf->active_readers) != 1);
+ atomic_long_dec(&ltt_buf->active_readers);
+ return 0;
+}
+
+static int get_subbuf(struct rchan_buf *buf, unsigned long *consumed)
+{
+ struct ltt_channel_struct *ltt_channel =
+ (struct ltt_channel_struct *)buf->chan->private_data;
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+ long consumed_old, consumed_idx, commit_count, write_offset;
+
+ WARN_ON(atomic_long_read(&ltt_buf->active_readers) != 1);
+
+ local_irq_disable();
+ __raw_spin_lock(&ltt_buf->lock);
+ consumed_old = ltt_buf->consumed;
+ consumed_idx = SUBBUF_INDEX(consumed_old, buf->chan);
+ commit_count = ltt_buf->commit_count[consumed_idx];
+ write_offset = ltt_buf->offset;
+ /*
+ * Check that the subbuffer we are trying to consume has been
+ * already fully committed.
+ */
+ if (((commit_count - buf->chan->subbuf_size)
+ & ltt_channel->commit_count_mask)
+ - (BUFFER_TRUNC(consumed_old, buf->chan)
+ >> ltt_channel->n_subbufs_order)
+ != 0) {
+ __raw_spin_unlock(&ltt_buf->lock);
+ local_irq_enable();
+ return -EAGAIN;
+ }
+ /*
+ * Check that we are not about to read the same subbuffer in
+ * which the writer head is.
+ */
+ if ((SUBBUF_TRUNC(write_offset, buf->chan)
+ - SUBBUF_TRUNC(consumed_old, buf->chan))
+ == 0) {
+ __raw_spin_unlock(&ltt_buf->lock);
+ local_irq_enable();
+ return -EAGAIN;
+ }
+ __raw_spin_unlock(&ltt_buf->lock);
+ local_irq_enable();
+ *consumed = consumed_old;
+ return 0;
+}
+
+static int put_subbuf(struct rchan_buf *buf, unsigned long consumed)
+{
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+ long consumed_new, consumed_old;
+
+ WARN_ON(atomic_long_read(&ltt_buf->active_readers) != 1);
+
+ local_irq_disable();
+ __raw_spin_lock(&ltt_buf->lock);
+ consumed_old = consumed;
+ consumed_new = SUBBUF_ALIGN(consumed_old, buf->chan);
+
+ if (ltt_buf->consumed != consumed_old) {
+ /* We have been pushed by the writer : the last
+ * buffer read _is_ corrupted! It can also
+ * happen if this is a buffer we never got. */
+ __raw_spin_unlock(&ltt_buf->lock);
+ local_irq_enable();
+ return -EIO;
+ } else {
+ /* tell the client that buffer is now unfull */
+ int index;
+ long data;
+
+ ltt_buf->consumed = consumed_new;
+ index = SUBBUF_INDEX(consumed_old, buf->chan);
+ data = BUFFER_OFFSET(consumed_old, buf->chan);
+ ltt_buf_unfull(buf, index, data);
+ __raw_spin_unlock(&ltt_buf->lock);
+ local_irq_enable();
+ }
+ return 0;
+}
+
+static unsigned long get_n_subbufs(struct rchan_buf *buf)
+{
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+
+ WARN_ON(atomic_long_read(&ltt_buf->active_readers) != 1);
+ return buf->chan->n_subbufs;
+}
+
+static unsigned long get_subbuf_size(struct rchan_buf *buf)
+{
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+
+ WARN_ON(atomic_long_read(&ltt_buf->active_readers) != 1);
+ return buf->chan->subbuf_size;
+}
+
+static struct ltt_channel_buf_access_ops ltt_channel_buf_accessor = {
+ .get_offset = get_offset,
+ .get_consumed = get_consumed,
+ .get_subbuf = get_subbuf,
+ .put_subbuf = put_subbuf,
+ .get_n_subbufs = get_n_subbufs,
+ .get_subbuf_size = get_subbuf_size,
+ .open = _ltt_open,
+ .release = _ltt_release,
+};
+
+/**
+ * ltt_open - open file op for ltt files
+ * @inode: opened inode
+ * @file: opened file
+ *
+ * Open implementation. Makes sure only one open instance of a buffer is
+ * done at a given moment.
+ */
+static int ltt_open(struct inode *inode, struct file *file)
+{
+ int ret;
+ struct rchan_buf *buf = inode->i_private;
+
+ ret = _ltt_open(buf);
+ if (!ret)
+ ret = ltt_relay_file_operations.open(inode, file);
+ return ret;
+}
+
+/**
+ * ltt_release - release file op for ltt files
+ * @inode: opened inode
+ * @file: opened file
+ *
+ * Release implementation.
+ */
+static int ltt_release(struct inode *inode, struct file *file)
+{
+ struct rchan_buf *buf = inode->i_private;
+ int ret;
+
+ _ltt_release(buf);
+ ret = ltt_relay_file_operations.release(inode, file);
+ WARN_ON(ret);
+ return ret;
+}
+
+/**
+ * ltt_poll - file op for ltt files
+ * @filp: the file
+ * @wait: poll table
+ *
+ * Poll implementation.
+ */
+static unsigned int ltt_poll(struct file *filp, poll_table *wait)
+{
+ unsigned int mask = 0, ret;
+ struct inode *inode = filp->f_dentry->d_inode;
+ struct rchan_buf *buf = inode->i_private;
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+
+ if (filp->f_mode & FMODE_READ) {
+ poll_wait_set_exclusive(wait);
+ poll_wait(filp, &ltt_buf->read_wait, wait);
+
+ local_irq_disable();
+ __raw_spin_lock(&ltt_buf->lock);
+ WARN_ON(atomic_long_read(&ltt_buf->active_readers) != 1);
+ if (SUBBUF_TRUNC(ltt_buf->offset, buf->chan)
+ - SUBBUF_TRUNC(ltt_buf->consumed, buf->chan)
+ == 0) {
+ if (ltt_buf->finalized)
+ ret = POLLHUP;
+ else
+ ret = 0;
+ goto end;
+ } else {
+ struct rchan *rchan = buf->chan;
+
+ if (SUBBUF_TRUNC(ltt_buf->offset, buf->chan)
+ - SUBBUF_TRUNC(ltt_buf->consumed, buf->chan)
+ >= rchan->alloc_size)
+ ret = POLLPRI | POLLRDBAND;
+ else
+ ret = POLLIN | POLLRDNORM;
+ goto end;
+ }
+end:
+ __raw_spin_unlock(&ltt_buf->lock);
+ local_irq_enable();
+ return ret;
+ }
+ return mask;
+}
+
+/**
+ * ltt_ioctl - control on the debugfs file
+ *
+ * @inode: the inode
+ * @filp: the file
+ * @cmd: the command
+ * @arg: command arg
+ *
+ * This ioctl implements three commands necessary for a minimal
+ * producer/consumer implementation :
+ * RELAY_GET_SUBBUF
+ * Get the next sub buffer that can be read. It never blocks.
+ * RELAY_PUT_SUBBUF
+ * Release the currently read sub-buffer. Parameter is the last
+ * put subbuffer (returned by GET_SUBBUF).
+ * RELAY_GET_N_BUBBUFS
+ * returns the number of sub buffers in the per cpu channel.
+ * RELAY_GET_SUBBUF_SIZE
+ * returns the size of the sub buffers.
+ */
+static int ltt_ioctl(struct inode *inode, struct file *filp,
+ unsigned int cmd, unsigned long arg)
+{
+ struct rchan_buf *buf = inode->i_private;
+ u32 __user *argp = (u32 __user *)arg;
+
+ switch (cmd) {
+ case RELAY_GET_SUBBUF:
+ {
+ unsigned long consumed;
+ int ret;
+
+ ret = get_subbuf(buf, &consumed);
+ if (ret)
+ return ret;
+ else
+ return put_user((u32)consumed, argp);
+ break;
+ }
+ case RELAY_PUT_SUBBUF:
+ {
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+ u32 uconsumed_old;
+ int ret;
+ long consumed_old;
+
+ ret = get_user(uconsumed_old, argp);
+ if (ret)
+ return ret; /* will return -EFAULT */
+
+ consumed_old = ltt_buf->consumed;
+ consumed_old = consumed_old & (~0xFFFFFFFFL);
+ consumed_old = consumed_old | uconsumed_old;
+ ret = put_subbuf(buf, consumed_old);
+ if (ret)
+ return ret;
+ break;
+ }
+ case RELAY_GET_N_SUBBUFS:
+ return put_user((u32)get_n_subbufs(buf), argp);
+ break;
+ case RELAY_GET_SUBBUF_SIZE:
+ return put_user((u32)get_subbuf_size(buf), argp);
+ break;
+ default:
+ return -ENOIOCTLCMD;
+ }
+ return 0;
+}
+
+#ifdef CONFIG_COMPAT
+static long ltt_compat_ioctl(struct file *file, unsigned int cmd,
+ unsigned long arg)
+{
+ long ret = -ENOIOCTLCMD;
+
+ lock_kernel();
+ ret = ltt_ioctl(file->f_dentry->d_inode, file, cmd, arg);
+ unlock_kernel();
+
+ return ret;
+}
+#endif
+
+static void ltt_relay_pipe_buf_release(struct pipe_inode_info *pipe,
+ struct pipe_buffer *pbuf)
+{
+}
+
+static struct pipe_buf_operations ltt_relay_pipe_buf_ops = {
+ .can_merge = 0,
+ .map = generic_pipe_buf_map,
+ .unmap = generic_pipe_buf_unmap,
+ .confirm = generic_pipe_buf_confirm,
+ .release = ltt_relay_pipe_buf_release,
+ .steal = generic_pipe_buf_steal,
+ .get = generic_pipe_buf_get,
+};
+
+static void ltt_relay_page_release(struct splice_pipe_desc *spd, unsigned int i)
+{
+}
+
+/*
+ * subbuf_splice_actor - splice up to one subbuf's worth of data
+ */
+static int subbuf_splice_actor(struct file *in,
+ loff_t *ppos,
+ struct pipe_inode_info *pipe,
+ size_t len,
+ unsigned int flags)
+{
+ struct rchan_buf *buf = in->private_data;
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+ unsigned int poff, subbuf_pages, nr_pages;
+ struct page *pages[PIPE_BUFFERS];
+ struct partial_page partial[PIPE_BUFFERS];
+ struct splice_pipe_desc spd = {
+ .pages = pages,
+ .nr_pages = 0,
+ .partial = partial,
+ .flags = flags,
+ .ops = &ltt_relay_pipe_buf_ops,
+ .spd_release = ltt_relay_page_release,
+ };
+ long consumed_old, consumed_idx, roffset;
+ unsigned long bytes_avail;
+
+ /*
+ * Check that a GET_SUBBUF ioctl has been done before.
+ */
+ local_irq_disable();
+ __raw_spin_lock(&ltt_buf->lock);
+ WARN_ON(atomic_long_read(&ltt_buf->active_readers) != 1);
+ consumed_old = ltt_buf->consumed;
+ consumed_old += *ppos;
+ consumed_idx = SUBBUF_INDEX(consumed_old, buf->chan);
+
+ /*
+ * Adjust read len, if longer than what is available
+ */
+ bytes_avail = SUBBUF_TRUNC(ltt_buf->offset, buf->chan) - consumed_old;
+ WARN_ON(bytes_avail > buf->chan->alloc_size);
+ len = min_t(size_t, len, bytes_avail);
+ subbuf_pages = bytes_avail >> PAGE_SHIFT;
+ nr_pages = min_t(unsigned int, subbuf_pages, PIPE_BUFFERS);
+ roffset = consumed_old & PAGE_MASK;
+ poff = consumed_old & ~PAGE_MASK;
+ printk_dbg(KERN_DEBUG "SPLICE actor len %zu pos %zd write_pos %ld\n",
+ len, (ssize_t)*ppos, ltt_buf->offset);
+
+ for (; spd.nr_pages < nr_pages; spd.nr_pages++) {
+ unsigned int this_len;
+ struct buf_page *page;
+
+ if (!len)
+ break;
+ printk_dbg(KERN_DEBUG "SPLICE actor loop len %zu roffset %ld\n",
+ len, roffset);
+
+ this_len = PAGE_SIZE - poff;
+ page = ltt_relay_read_get_page(buf, roffset);
+ spd.pages[spd.nr_pages] = page->page;
+ spd.partial[spd.nr_pages].offset = poff;
+ spd.partial[spd.nr_pages].len = this_len;
+
+ poff = 0;
+ roffset += PAGE_SIZE;
+ len -= this_len;
+ }
+ __raw_spin_unlock(&ltt_buf->lock);
+ local_irq_enable();
+
+ if (!spd.nr_pages)
+ return 0;
+
+ return splice_to_pipe(pipe, &spd);
+}
+
+static ssize_t ltt_relay_file_splice_read(struct file *in,
+ loff_t *ppos,
+ struct pipe_inode_info *pipe,
+ size_t len,
+ unsigned int flags)
+{
+ ssize_t spliced;
+ int ret;
+
+ ret = 0;
+ spliced = 0;
+
+ printk_dbg(KERN_DEBUG "SPLICE read len %zu pos %zd\n",
+ len, (ssize_t)*ppos);
+ while (len && !spliced) {
+ ret = subbuf_splice_actor(in, ppos, pipe, len, flags);
+ printk_dbg(KERN_DEBUG "SPLICE read loop ret %d\n", ret);
+ if (ret < 0)
+ break;
+ else if (!ret) {
+ if (flags & SPLICE_F_NONBLOCK)
+ ret = -EAGAIN;
+ break;
+ }
+
+ *ppos += ret;
+ if (ret > len)
+ len = 0;
+ else
+ len -= ret;
+ spliced += ret;
+ }
+
+ if (spliced)
+ return spliced;
+
+ return ret;
+}
+
+static void ltt_relay_print_subbuffer_errors(
+ struct ltt_channel_struct *ltt_chan,
+ long cons_off, unsigned int cpu)
+{
+ struct rchan *rchan = ltt_chan->trans_channel_data;
+ struct ltt_channel_buf_struct *ltt_buf = rchan->buf[cpu]->chan_private;
+ long cons_idx, commit_count, write_offset;
+
+ cons_idx = SUBBUF_INDEX(cons_off, rchan);
+ commit_count = ltt_buf->commit_count[cons_idx];
+ write_offset = ltt_buf->offset;
+ printk(KERN_WARNING
+ "LTT : unread channel %s offset is %ld "
+ "and cons_off : %ld (cpu %u)\n",
+ ltt_chan->channel_name, write_offset, cons_off, cpu);
+ /* Check each sub-buffer for non filled commit count */
+ if (((commit_count - rchan->subbuf_size) & ltt_chan->commit_count_mask)
+ - (BUFFER_TRUNC(cons_off, rchan) >> ltt_chan->n_subbufs_order)
+ != 0)
+ printk(KERN_ALERT
+ "LTT : %s : subbuffer %lu has non filled "
+ "commit count %lu.\n",
+ ltt_chan->channel_name, cons_idx, commit_count);
+ printk(KERN_ALERT "LTT : %s : commit count : %lu, subbuf size %zd\n",
+ ltt_chan->channel_name, commit_count,
+ rchan->subbuf_size);
+}
+
+static void ltt_relay_print_errors(struct ltt_trace_struct *trace,
+ struct ltt_channel_struct *ltt_chan, int cpu)
+{
+ struct rchan *rchan = ltt_chan->trans_channel_data;
+ struct ltt_channel_buf_struct *ltt_buf = rchan->buf[cpu]->chan_private;
+ long cons_off;
+
+ /*
+ * Can be called in the error path of allocation when
+ * trans_channel_data is not yet set.
+ */
+ if (!rchan)
+ return;
+ for (cons_off = ltt_buf->consumed;
+ (SUBBUF_TRUNC(ltt_buf->offset, rchan) - cons_off) > 0;
+ cons_off = SUBBUF_ALIGN(cons_off, rchan))
+ ltt_relay_print_subbuffer_errors(ltt_chan, cons_off, cpu);
+}
+
+static void ltt_relay_print_buffer_errors(struct ltt_channel_struct *ltt_chan,
+ unsigned int cpu)
+{
+ struct ltt_trace_struct *trace = ltt_chan->trace;
+ struct rchan *rchan = ltt_chan->trans_channel_data;
+ struct ltt_channel_buf_struct *ltt_buf = rchan->buf[cpu]->chan_private;
+
+ if (ltt_buf->events_lost)
+ printk(KERN_ALERT
+ "LTT : %s : %ld events lost "
+ "in %s channel (cpu %u).\n",
+ ltt_chan->channel_name,
+ ltt_buf->events_lost,
+ ltt_chan->channel_name, cpu);
+ if (ltt_buf->corrupted_subbuffers)
+ printk(KERN_ALERT
+ "LTT : %s : %ld corrupted subbuffers "
+ "in %s channel (cpu %u).\n",
+ ltt_chan->channel_name,
+ ltt_buf->corrupted_subbuffers,
+ ltt_chan->channel_name, cpu);
+
+ ltt_relay_print_errors(trace, ltt_chan, cpu);
+}
+
+static void ltt_relay_remove_dirs(struct ltt_trace_struct *trace)
+{
+ debugfs_remove(trace->dentry.trace_root);
+}
+
+/*
+ * Create ltt buffer.
+ */
+static int ltt_relay_create_buffer(struct ltt_trace_struct *trace,
+ struct ltt_channel_struct *ltt_chan, struct rchan_buf *buf,
+ unsigned int cpu, unsigned int n_subbufs)
+{
+ struct ltt_channel_buf_struct *ltt_buf;
+ ltt_buf = kzalloc_node(sizeof(*ltt_buf), GFP_KERNEL, cpu_to_node(cpu));
+ if (!ltt_buf)
+ return -ENOMEM;
+
+ ltt_buf->commit_count =
+ kzalloc_node(sizeof(ltt_buf->commit_count) * n_subbufs,
+ GFP_KERNEL, cpu_to_node(cpu));
+ if (!ltt_buf->commit_count) {
+ kfree(ltt_buf);
+ return -ENOMEM;
+ }
+ buf->chan_private = ltt_buf;
+
+ kref_get(&trace->kref);
+ kref_get(&trace->ltt_transport_kref);
+ ltt_buf->offset = ltt_subbuffer_header_size();
+ atomic_long_set(&ltt_buf->active_readers, 0);
+ init_waitqueue_head(&ltt_buf->write_wait);
+ init_waitqueue_head(&ltt_buf->read_wait);
+ ltt_buffer_begin_callback(buf, trace->start_tsc, 0);
+ ltt_buf->commit_count[0] += ltt_subbuffer_header_size();
+ ltt_buf->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
+
+ return 0;
+}
+
+static void ltt_relay_destroy_buffer(struct ltt_channel_struct *ltt_chan,
+ unsigned int cpu)
+{
+ struct ltt_trace_struct *trace = ltt_chan->trace;
+ struct rchan *rchan = ltt_chan->trans_channel_data;
+ struct ltt_channel_buf_struct *ltt_buf = rchan->buf[cpu]->chan_private;
+
+ kref_put(&ltt_chan->trace->ltt_transport_kref,
+ ltt_release_transport);
+ ltt_relay_print_buffer_errors(ltt_chan, cpu);
+ kfree(ltt_buf->commit_count);
+ kfree(ltt_buf);
+ kref_put(&trace->kref, ltt_release_trace);
+ wake_up_interruptible(&trace->kref_wq);
+}
+
+/*
+ * Create channel.
+ */
+static int ltt_relay_create_channel(const char *trace_name,
+ struct ltt_trace_struct *trace, struct dentry *dir,
+ const char *channel_name, struct ltt_channel_struct *ltt_chan,
+ unsigned int subbuf_size, unsigned int n_subbufs,
+ int overwrite)
+{
+ char *tmpname;
+ unsigned int tmpname_len;
+ int err = 0;
+
+ tmpname = kmalloc(PATH_MAX, GFP_KERNEL);
+ if (!tmpname)
+ return EPERM;
+ if (overwrite) {
+ strncpy(tmpname, LTT_FLIGHT_PREFIX, PATH_MAX-1);
+ strncat(tmpname, channel_name,
+ PATH_MAX-1-sizeof(LTT_FLIGHT_PREFIX));
+ } else {
+ strncpy(tmpname, channel_name, PATH_MAX-1);
+ }
+ strncat(tmpname, "_", PATH_MAX-1-strlen(tmpname));
+
+ ltt_chan->trace = trace;
+ ltt_chan->buffer_begin = ltt_buffer_begin_callback;
+ ltt_chan->buffer_end = ltt_buffer_end_callback;
+ ltt_chan->overwrite = overwrite;
+ ltt_chan->n_subbufs_order = get_count_order(n_subbufs);
+ ltt_chan->commit_count_mask = (~0UL >> ltt_chan->n_subbufs_order);
+ ltt_chan->trans_channel_data = ltt_relay_open(tmpname,
+ dir,
+ subbuf_size,
+ n_subbufs,
+ &trace->callbacks,
+ ltt_chan);
+ tmpname_len = strlen(tmpname);
+ if (tmpname_len > 0) {
+ /* Remove final _ for pretty printing */
+ tmpname[tmpname_len-1] = '\0';
+ }
+ if (ltt_chan->trans_channel_data == NULL) {
+ printk(KERN_ERR "LTT : Can't open %s channel for trace %s\n",
+ tmpname, trace_name);
+ goto relay_open_error;
+ }
+
+ ltt_chan->buf_access_ops = &ltt_channel_buf_accessor;
+
+ err = 0;
+ goto end;
+
+relay_open_error:
+ err = EPERM;
+end:
+ kfree(tmpname);
+ return err;
+}
+
+static int ltt_relay_create_dirs(struct ltt_trace_struct *new_trace)
+{
+ struct dentry *ltt_root_dentry;
+
+ ltt_root_dentry = get_ltt_root();
+ if (!ltt_root_dentry)
+ return ENOENT;
+
+ new_trace->dentry.trace_root = debugfs_create_dir(new_trace->trace_name,
+ ltt_root_dentry);
+ put_ltt_root();
+ if (new_trace->dentry.trace_root == NULL) {
+ printk(KERN_ERR "LTT : Trace directory name %s already taken\n",
+ new_trace->trace_name);
+ return EEXIST;
+ }
+
+ new_trace->callbacks.create_buf_file = ltt_create_buf_file_callback;
+ new_trace->callbacks.remove_buf_file = ltt_remove_buf_file_callback;
+
+ return 0;
+}
+
+/*
+ * LTTng channel flush function.
+ *
+ * Must be called when no tracing is active in the channel, because of
+ * accesses across CPUs.
+ */
+static notrace void ltt_relay_buffer_flush(struct rchan_buf *buf)
+{
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+
+ ltt_buf->finalized = 1;
+ ltt_force_switch(buf, FORCE_FLUSH);
+}
+
+static void ltt_relay_async_wakeup_chan(struct ltt_channel_struct *ltt_channel)
+{
+ unsigned int i;
+ struct rchan *rchan = ltt_channel->trans_channel_data;
+
+ for_each_possible_cpu(i) {
+ struct ltt_channel_buf_struct *ltt_buf;
+
+ if (!rchan->buf[i])
+ continue;
+
+ ltt_buf = rchan->buf[i]->chan_private;
+ if (ltt_buf->wakeup_readers == 1) {
+ ltt_buf->wakeup_readers = 0;
+ wake_up_interruptible(&ltt_buf->read_wait);
+ }
+ }
+}
+
+static void ltt_relay_finish_buffer(struct ltt_channel_struct *ltt_channel,
+ unsigned int cpu)
+{
+ struct rchan *rchan = ltt_channel->trans_channel_data;
+
+ if (rchan->buf[cpu]) {
+ struct ltt_channel_buf_struct *ltt_buf =
+ rchan->buf[cpu]->chan_private;
+ ltt_relay_buffer_flush(rchan->buf[cpu]);
+ ltt_relay_wake_writers(ltt_buf);
+ }
+}
+
+
+static void ltt_relay_finish_channel(struct ltt_channel_struct *ltt_channel)
+{
+ unsigned int i;
+
+ for_each_possible_cpu(i)
+ ltt_relay_finish_buffer(ltt_channel, i);
+}
+
+static void ltt_relay_remove_channel(struct ltt_channel_struct *channel)
+{
+ struct rchan *rchan = channel->trans_channel_data;
+
+ ltt_relay_close(rchan);
+}
+
+struct ltt_reserve_switch_offsets {
+ long begin, end, old;
+ long begin_switch, end_switch_current, end_switch_old;
+ long commit_count, reserve_commit_diff;
+ size_t before_hdr_pad, size;
+};
+
+/*
+ * Returns :
+ * 0 if ok
+ * !0 if execution must be aborted.
+ */
+static inline int ltt_relay_try_reserve(
+ struct ltt_channel_struct *ltt_channel,
+ struct ltt_channel_buf_struct *ltt_buf, struct rchan *rchan,
+ struct rchan_buf *buf,
+ struct ltt_reserve_switch_offsets *offsets, size_t data_size,
+ u64 *tsc, unsigned int *rflags, int largest_align)
+{
+ offsets->begin = ltt_buf->offset;
+ offsets->old = offsets->begin;
+ offsets->begin_switch = 0;
+ offsets->end_switch_current = 0;
+ offsets->end_switch_old = 0;
+
+ *tsc = trace_clock_read64();
+ if (last_tsc_overflow(ltt_buf, *tsc))
+ *rflags = LTT_RFLAG_ID_SIZE_TSC;
+
+ if (SUBBUF_OFFSET(offsets->begin, buf->chan) == 0) {
+ offsets->begin_switch = 1; /* For offsets->begin */
+ } else {
+ offsets->size = ltt_get_header_size(ltt_channel,
+ offsets->begin, data_size,
+ &offsets->before_hdr_pad, *rflags);
+ offsets->size += ltt_align(offsets->begin + offsets->size,
+ largest_align)
+ + data_size;
+ if ((SUBBUF_OFFSET(offsets->begin, buf->chan) + offsets->size)
+ > buf->chan->subbuf_size) {
+ offsets->end_switch_old = 1; /* For offsets->old */
+ offsets->begin_switch = 1; /* For offsets->begin */
+ }
+ }
+ if (offsets->begin_switch) {
+ long subbuf_index;
+
+ if (offsets->end_switch_old)
+ offsets->begin = SUBBUF_ALIGN(offsets->begin,
+ buf->chan);
+ offsets->begin = offsets->begin + ltt_subbuffer_header_size();
+ /* Test new buffer integrity */
+ subbuf_index = SUBBUF_INDEX(offsets->begin, buf->chan);
+ offsets->reserve_commit_diff =
+ (BUFFER_TRUNC(offsets->begin, buf->chan)
+ >> ltt_channel->n_subbufs_order)
+ - (ltt_buf->commit_count[subbuf_index]
+ & ltt_channel->commit_count_mask);
+ if (offsets->reserve_commit_diff == 0) {
+ /* Next buffer not corrupted. */
+ if (!ltt_channel->overwrite &&
+ (SUBBUF_TRUNC(offsets->begin, buf->chan)
+ - SUBBUF_TRUNC(ltt_buf->consumed, buf->chan))
+ >= rchan->alloc_size) {
+ /*
+ * We do not overwrite non consumed buffers
+ * and we are full : event is lost.
+ */
+ ltt_buf->events_lost++;
+ return -1;
+ } else {
+ /*
+ * next buffer not corrupted, we are either in
+ * overwrite mode or the buffer is not full.
+ * It's safe to write in this new subbuffer.
+ */
+ }
+ } else {
+ /*
+ * Next subbuffer corrupted. Force pushing reader even
+ * in normal mode. It's safe to write in this new
+ * subbuffer.
+ */
+ }
+ offsets->size = ltt_get_header_size(ltt_channel,
+ offsets->begin, data_size,
+ &offsets->before_hdr_pad, *rflags);
+ offsets->size += ltt_align(offsets->begin + offsets->size,
+ largest_align)
+ + data_size;
+ if ((SUBBUF_OFFSET(offsets->begin, buf->chan) + offsets->size)
+ > buf->chan->subbuf_size) {
+ /*
+ * Event too big for subbuffers, report error, don't
+ * complete the sub-buffer switch.
+ */
+ ltt_buf->events_lost++;
+ return -1;
+ } else {
+ /*
+ * We just made a successful buffer switch and the event
+ * fits in the new subbuffer. Let's write.
+ */
+ }
+ } else {
+ /*
+ * Event fits in the current buffer and we are not on a switch
+ * boundary. It's safe to write.
+ */
+ }
+ offsets->end = offsets->begin + offsets->size;
+
+ if ((SUBBUF_OFFSET(offsets->end, buf->chan)) == 0) {
+ /*
+ * The offset_end will fall at the very beginning of the next
+ * subbuffer.
+ */
+ offsets->end_switch_current = 1; /* For offsets->begin */
+ }
+ return 0;
+}
+
+/*
+ * Returns :
+ * 0 if ok
+ * !0 if execution must be aborted.
+ */
+static inline int ltt_relay_try_switch(
+ enum force_switch_mode mode,
+ struct ltt_channel_struct *ltt_channel,
+ struct ltt_channel_buf_struct *ltt_buf, struct rchan *rchan,
+ struct rchan_buf *buf,
+ struct ltt_reserve_switch_offsets *offsets,
+ u64 *tsc)
+{
+ long subbuf_index;
+
+ offsets->begin = ltt_buf->offset;
+ offsets->old = offsets->begin;
+ offsets->begin_switch = 0;
+ offsets->end_switch_old = 0;
+
+ *tsc = trace_clock_read64();
+
+ if (SUBBUF_OFFSET(offsets->begin, buf->chan) != 0) {
+ offsets->begin = SUBBUF_ALIGN(offsets->begin, buf->chan);
+ offsets->end_switch_old = 1;
+ } else {
+ /* we do not have to switch : buffer is empty */
+ return -1;
+ }
+ if (mode == FORCE_ACTIVE)
+ offsets->begin += ltt_subbuffer_header_size();
+ /*
+ * Always begin_switch in FORCE_ACTIVE mode.
+ * Test new buffer integrity
+ */
+ subbuf_index = SUBBUF_INDEX(offsets->begin, buf->chan);
+ offsets->reserve_commit_diff =
+ (BUFFER_TRUNC(offsets->begin, buf->chan)
+ >> ltt_channel->n_subbufs_order)
+ - (ltt_buf->commit_count[subbuf_index]
+ & ltt_channel->commit_count_mask);
+ if (offsets->reserve_commit_diff == 0) {
+ /* Next buffer not corrupted. */
+ if (mode == FORCE_ACTIVE
+ && !ltt_channel->overwrite
+ && offsets->begin - ltt_buf->consumed
+ >= rchan->alloc_size) {
+ /*
+ * We do not overwrite non consumed buffers and we are
+ * full : ignore switch while tracing is active.
+ */
+ return -1;
+ }
+ } else {
+ /*
+ * Next subbuffer corrupted. Force pushing reader even in normal
+ * mode
+ */
+ }
+ offsets->end = offsets->begin;
+ return 0;
+}
+
+static inline void ltt_reserve_push_reader(
+ struct ltt_channel_struct *ltt_channel,
+ struct ltt_channel_buf_struct *ltt_buf,
+ struct rchan *rchan,
+ struct rchan_buf *buf,
+ struct ltt_reserve_switch_offsets *offsets)
+{
+ long consumed_old, consumed_new;
+
+ consumed_old = ltt_buf->consumed;
+ /*
+ * If buffer is in overwrite mode, push the reader consumed
+ * count if the write position has reached it and we are not
+ * at the first iteration (don't push the reader farther than
+ * the writer). This operation can be done concurrently by many
+ * writers in the same buffer, the writer being at the farthest
+ * write position sub-buffer index in the buffer being the one
+ * which will win this loop.
+ * If the buffer is not in overwrite mode, pushing the reader
+ * only happens if a sub-buffer is corrupted.
+ */
+ if ((SUBBUF_TRUNC(offsets->end-1, buf->chan)
+ - SUBBUF_TRUNC(consumed_old, buf->chan))
+ >= rchan->alloc_size) {
+ consumed_new = SUBBUF_ALIGN(consumed_old, buf->chan);
+ ltt_buf->consumed = consumed_new;
+ } else
+ consumed_new = consumed_old;
+
+ if (consumed_old != consumed_new) {
+ /*
+ * Reader pushed : we are the winner of the push, we can
+ * therefore reequilibrate reserve and commit. Atomic increment
+ * of the commit count permits other writers to play around
+ * with this variable before us. We keep track of
+ * corrupted_subbuffers even in overwrite mode :
+ * we never want to write over a non completely committed
+ * sub-buffer : possible causes : the buffer size is too low
+ * compared to the unordered data input, or there is a writer
+ * that died between the reserve and the commit.
+ */
+ if (offsets->reserve_commit_diff) {
+ /*
+ * We have to alter the sub-buffer commit count.
+ * We do not deliver the previous subbuffer, given it
+ * was either corrupted or not consumed (overwrite
+ * mode).
+ */
+ ltt_buf->commit_count[SUBBUF_INDEX(offsets->begin,
+ buf->chan)] +=
+ offsets->reserve_commit_diff;
+ if (!ltt_channel->overwrite
+ || offsets->reserve_commit_diff
+ != rchan->subbuf_size) {
+ /*
+ * The reserve commit diff was not subbuf_size :
+ * it means the subbuffer was partly written to
+ * and is therefore corrupted. If it is multiple
+ * of subbuffer size and we are in flight
+ * recorder mode, we are skipping over a whole
+ * subbuffer.
+ */
+ ltt_buf->corrupted_subbuffers++;
+ }
+ }
+ }
+}
+
+
+/*
+ * ltt_reserve_switch_old_subbuf: switch old subbuffer
+ *
+ * Concurrency safe because we are the last and only thread to alter this
+ * sub-buffer. As long as it is not delivered and read, no other thread can
+ * alter the offset, alter the reserve_count or call the
+ * client_buffer_end_callback on this sub-buffer.
+ *
+ * The only remaining threads could be the ones with pending commits. They will
+ * have to do the deliver themselves. Not concurrency safe in overwrite mode.
+ * We detect corrupted subbuffers with commit and reserve counts. We keep a
+ * corrupted sub-buffers count and push the readers across these sub-buffers.
+ *
+ * Not concurrency safe if a writer is stalled in a subbuffer and another writer
+ * switches in, finding out it's corrupted. The result will be than the old
+ * (uncommited) subbuffer will be declared corrupted, and that the new subbuffer
+ * will be declared corrupted too because of the commit count adjustment.
+ *
+ * Note : offset_old should never be 0 here.
+ */
+static inline void ltt_reserve_switch_old_subbuf(
+ struct ltt_channel_struct *ltt_channel,
+ struct ltt_channel_buf_struct *ltt_buf, struct rchan *rchan,
+ struct rchan_buf *buf,
+ struct ltt_reserve_switch_offsets *offsets, u64 *tsc)
+{
+ long oldidx = SUBBUF_INDEX(offsets->old - 1, rchan);
+
+ ltt_channel->buffer_end(buf, *tsc, offsets->old, oldidx);
+ ltt_buf->commit_count[oldidx] +=
+ rchan->subbuf_size
+ - (SUBBUF_OFFSET(offsets->old - 1, rchan)
+ + 1);
+ offsets->commit_count = ltt_buf->commit_count[oldidx];
+ if ((BUFFER_TRUNC(offsets->old - 1, rchan)
+ >> ltt_channel->n_subbufs_order)
+ - ((offsets->commit_count - rchan->subbuf_size)
+ & ltt_channel->commit_count_mask) == 0)
+ ltt_deliver(buf, oldidx, NULL);
+}
+
+/*
+ * ltt_reserve_switch_new_subbuf: Populate new subbuffer.
+ *
+ * This code can be executed unordered : writers may already have written to the
+ * sub-buffer before this code gets executed, caution. The commit makes sure
+ * that this code is executed before the deliver of this sub-buffer.
+ */
+static inline void ltt_reserve_switch_new_subbuf(
+ struct ltt_channel_struct *ltt_channel,
+ struct ltt_channel_buf_struct *ltt_buf, struct rchan *rchan,
+ struct rchan_buf *buf,
+ struct ltt_reserve_switch_offsets *offsets, u64 *tsc)
+{
+ long beginidx = SUBBUF_INDEX(offsets->begin, rchan);
+
+ ltt_channel->buffer_begin(buf, *tsc, beginidx);
+ ltt_buf->commit_count[beginidx] += ltt_subbuffer_header_size();
+ offsets->commit_count = ltt_buf->commit_count[beginidx];
+ /* Check if the written buffer has to be delivered */
+ if ((BUFFER_TRUNC(offsets->end - 1, rchan)
+ >> ltt_channel->n_subbufs_order)
+ - ((offsets->commit_count - rchan->subbuf_size)
+ & ltt_channel->commit_count_mask) == 0)
+ ltt_deliver(buf, beginidx, NULL);
+}
+
+
+/*
+ * ltt_reserve_end_switch_current: finish switching current subbuffer
+ *
+ * Concurrency safe because we are the last and only thread to alter this
+ * sub-buffer. As long as it is not delivered and read, no other thread can
+ * alter the offset, alter the reserve_count or call the
+ * client_buffer_end_callback on this sub-buffer.
+ *
+ * The only remaining threads could be the ones with pending commits. They will
+ * have to do the deliver themselves. Not concurrency safe in overwrite mode.
+ * We detect corrupted subbuffers with commit and reserve counts. We keep a
+ * corrupted sub-buffers count and push the readers across these sub-buffers.
+ *
+ * Not concurrency safe if a writer is stalled in a subbuffer and another writer
+ * switches in, finding out it's corrupted. The result will be than the old
+ * (uncommited) subbuffer will be declared corrupted, and that the new subbuffer
+ * will be declared corrupted too because of the commit count adjustment.
+ */
+static inline void ltt_reserve_end_switch_current(
+ struct ltt_channel_struct *ltt_channel,
+ struct ltt_channel_buf_struct *ltt_buf, struct rchan *rchan,
+ struct rchan_buf *buf,
+ struct ltt_reserve_switch_offsets *offsets, u64 *tsc)
+{
+ long endidx = SUBBUF_INDEX(offsets->end - 1, rchan);
+
+ ltt_channel->buffer_end(buf, *tsc, offsets->end, endidx);
+ ltt_buf->commit_count[endidx] +=
+ rchan->subbuf_size
+ - (SUBBUF_OFFSET(offsets->end - 1, rchan)
+ + 1);
+ offsets->commit_count = ltt_buf->commit_count[endidx];
+ if ((BUFFER_TRUNC(offsets->end - 1, rchan)
+ >> ltt_channel->n_subbufs_order)
+ - ((offsets->commit_count - rchan->subbuf_size)
+ & ltt_channel->commit_count_mask) == 0)
+ ltt_deliver(buf, endidx, NULL);
+}
+
+/**
+ * ltt_relay_reserve_slot - Atomic slot reservation in a LTTng buffer.
+ * @trace : the trace structure to log to.
+ * @ltt_channel : channel structure
+ * @transport_data : data structure specific to ltt relay
+ * @data_size : size of the variable length data to log.
+ * @slot_size : pointer to total size of the slot (out)
+ * @buf_offset : pointer to reserved buffer offset (out)
+ * @tsc : pointer to the tsc at the slot reservation (out)
+ * @cpu : cpuid
+ *
+ * Return : -ENOSPC if not enough space, else returns 0.
+ *
+ * It will take care of sub-buffer switching.
+ */
+static notrace int ltt_relay_reserve_slot(struct ltt_trace_struct *trace,
+ struct ltt_channel_struct *ltt_channel, void **transport_data,
+ size_t data_size, size_t *slot_size, long *buf_offset, u64 *tsc,
+ unsigned int *rflags, int largest_align, int cpu)
+{
+ struct rchan *rchan = ltt_channel->trans_channel_data;
+ struct rchan_buf *buf = *transport_data = rchan->buf[cpu];
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+ struct ltt_reserve_switch_offsets offsets;
+ unsigned long flags;
+
+ raw_local_irq_save(flags);
+ __raw_spin_lock(&ltt_buf->lock);
+
+ offsets.reserve_commit_diff = 0;
+ offsets.size = 0;
+
+ /*
+ * Perform retryable operations.
+ */
+ if (__get_cpu_var(ltt_nesting) > 4) {
+ ltt_buf->events_lost++;
+ __raw_spin_unlock(&ltt_buf->lock);
+ raw_local_irq_restore(flags);
+ return -EPERM;
+ }
+
+ if (ltt_relay_try_reserve(ltt_channel, ltt_buf,
+ rchan, buf, &offsets, data_size, tsc, rflags,
+ largest_align)) {
+ __raw_spin_unlock(&ltt_buf->lock);
+ raw_local_irq_restore(flags);
+ return -ENOSPC;
+ }
+ ltt_buf->offset = offsets.end;
+
+ save_last_tsc(ltt_buf, *tsc);
+
+ /*
+ * Push the reader if necessary
+ */
+ ltt_reserve_push_reader(ltt_channel, ltt_buf, rchan, buf, &offsets);
+
+ /*
+ * Switch old subbuffer if needed.
+ */
+ if (offsets.end_switch_old)
+ ltt_reserve_switch_old_subbuf(ltt_channel, ltt_buf, rchan, buf,
+ &offsets, tsc);
+
+ /*
+ * Populate new subbuffer.
+ */
+ if (offsets.begin_switch)
+ ltt_reserve_switch_new_subbuf(ltt_channel, ltt_buf, rchan,
+ buf, &offsets, tsc);
+
+ if (offsets.end_switch_current)
+ ltt_reserve_end_switch_current(ltt_channel, ltt_buf, rchan,
+ buf, &offsets, tsc);
+
+ ltt_buf->irqflags = flags;
+ *slot_size = offsets.size;
+ *buf_offset = offsets.begin + offsets.before_hdr_pad;
+ return 0;
+}
+
+/*
+ * Force a sub-buffer switch for a per-cpu buffer. This operation is
+ * completely reentrant : can be called while tracing is active with
+ * absolutely no lock held.
+ */
+static notrace void ltt_force_switch(struct rchan_buf *buf,
+ enum force_switch_mode mode)
+{
+ struct ltt_channel_struct *ltt_channel =
+ (struct ltt_channel_struct *)buf->chan->private_data;
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+ struct rchan *rchan = ltt_channel->trans_channel_data;
+ struct ltt_reserve_switch_offsets offsets;
+ unsigned long flags;
+ u64 tsc;
+
+ offsets.reserve_commit_diff = 0;
+ offsets.size = 0;
+
+ raw_local_irq_save(flags);
+ __raw_spin_lock(&ltt_buf->lock);
+
+ /*
+ * Perform retryable operations.
+ */
+ if (ltt_relay_try_switch(mode, ltt_channel, ltt_buf,
+ rchan, buf, &offsets, &tsc)) {
+ __raw_spin_unlock(&ltt_buf->lock);
+ raw_local_irq_restore(flags);
+ return;
+ }
+ ltt_buf->offset = offsets.end;
+
+ save_last_tsc(ltt_buf, tsc);
+
+ /*
+ * Push the reader if necessary
+ */
+ if (mode == FORCE_ACTIVE)
+ ltt_reserve_push_reader(ltt_channel, ltt_buf, rchan,
+ buf, &offsets);
+
+ /*
+ * Switch old subbuffer if needed.
+ */
+ if (offsets.end_switch_old)
+ ltt_reserve_switch_old_subbuf(ltt_channel, ltt_buf, rchan, buf,
+ &offsets, &tsc);
+
+ /*
+ * Populate new subbuffer.
+ */
+ if (mode == FORCE_ACTIVE)
+ ltt_reserve_switch_new_subbuf(ltt_channel,
+ ltt_buf, rchan, buf, &offsets, &tsc);
+
+ __raw_spin_unlock(&ltt_buf->lock);
+ raw_local_irq_restore(flags);
+}
+
+/*
+ * for flight recording. must be called after relay_commit.
+ * This function decrements de subbuffer's lost_size each time the commit count
+ * reaches back the reserve offset (module subbuffer size). It is useful for
+ * crash dump.
+ * We use slot_size - 1 to make sure we deal correctly with the case where we
+ * fill the subbuffer completely (so the subbuf index stays in the previous
+ * subbuffer).
+ */
+#ifdef CONFIG_LTT_VMCORE
+static inline void ltt_write_commit_counter(struct rchan_buf *buf,
+ long buf_offset, size_t slot_size)
+{
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+ struct ltt_subbuffer_header *header;
+ long offset, subbuf_idx, commit_count;
+ uint32_t lost_old, lost_new;
+
+ subbuf_idx = SUBBUF_INDEX(buf_offset - 1, buf->chan);
+ offset = buf_offset + slot_size;
+ header = (struct ltt_subbuffer_header *)
+ ltt_relay_offset_address(buf,
+ subbuf_idx * buf->chan->subbuf_size);
+ for (;;) {
+ lost_old = header->lost_size;
+ commit_count = ltt_buf->commit_count[subbuf_idx];
+ /* SUBBUF_OFFSET includes commit_count_mask */
+ if (!SUBBUF_OFFSET(offset - commit_count, buf->chan)) {
+ lost_new = (uint32_t)buf->chan->subbuf_size
+ - SUBBUF_OFFSET(commit_count, buf->chan);
+ lost_old = cmpxchg_local(&header->lost_size, lost_old,
+ lost_new);
+ if (lost_old <= lost_new)
+ break;
+ } else {
+ break;
+ }
+ }
+}
+#else
+static inline void ltt_write_commit_counter(struct rchan_buf *buf,
+ long buf_offset, size_t slot_size)
+{
+}
+#endif
+
+/*
+ * Atomic unordered slot commit. Increments the commit count in the
+ * specified sub-buffer, and delivers it if necessary.
+ *
+ * Parameters:
+ *
+ * @ltt_channel : channel structure
+ * @transport_data: transport-specific data
+ * @buf_offset : offset following the event header.
+ * @slot_size : size of the reserved slot.
+ */
+static notrace void ltt_relay_commit_slot(
+ struct ltt_channel_struct *ltt_channel,
+ void **transport_data, long buf_offset, size_t slot_size)
+{
+ struct rchan_buf *buf = *transport_data;
+ struct ltt_channel_buf_struct *ltt_buf = buf->chan_private;
+ struct rchan *rchan = buf->chan;
+ unsigned int offset_end = buf_offset;
+ long endidx = SUBBUF_INDEX(offset_end - 1, rchan);
+ long commit_count;
+
+ ltt_buf->commit_count[endidx] += slot_size;
+ commit_count = ltt_buf->commit_count[endidx];
+ /* Check if all commits have been done */
+ if ((BUFFER_TRUNC(offset_end - 1, rchan)
+ >> ltt_channel->n_subbufs_order)
+ - ((commit_count - rchan->subbuf_size)
+ & ltt_channel->commit_count_mask) == 0)
+ ltt_deliver(buf, endidx, NULL);
+ /*
+ * Update lost_size for each commit. It's needed only for extracting
+ * ltt buffers from vmcore, after crash.
+ */
+ ltt_write_commit_counter(buf, buf_offset, slot_size);
+ __raw_spin_unlock(&ltt_buf->lock);
+ raw_local_irq_restore(ltt_buf->irqflags);
+}
+
+/*
+ * This is called with preemption disabled when user space has requested
+ * blocking mode. If one of the active traces has free space below a
+ * specific threshold value, we reenable preemption and block.
+ */
+static int ltt_relay_user_blocking(struct ltt_trace_struct *trace,
+ unsigned int chan_index, size_t data_size,
+ struct user_dbg_data *dbg)
+{
+ struct rchan *rchan;
+ struct ltt_channel_buf_struct *ltt_buf;
+ struct ltt_channel_struct *channel;
+ struct rchan_buf *relay_buf;
+ int cpu;
+ DECLARE_WAITQUEUE(wait, current);
+
+ channel = &trace->channels[chan_index];
+ rchan = channel->trans_channel_data;
+ cpu = smp_processor_id();
+ relay_buf = rchan->buf[cpu];
+ ltt_buf = relay_buf->chan_private;
+
+ /*
+ * Check if data is too big for the channel : do not
+ * block for it.
+ */
+ if (LTT_RESERVE_CRITICAL + data_size > relay_buf->chan->subbuf_size)
+ return 0;
+
+ /*
+ * If free space too low, we block. We restart from the
+ * beginning after we resume (cpu id may have changed
+ * while preemption is active).
+ */
+ local_irq_disable();
+ __raw_spin_lock(&ltt_buf->lock);
+ if (!channel->overwrite) {
+ dbg->write = ltt_buf->offset;
+ dbg->read = ltt_buf->consumed;
+ dbg->avail_size = dbg->write + LTT_RESERVE_CRITICAL + data_size
+ - SUBBUF_TRUNC(dbg->read,
+ relay_buf->chan);
+ if (dbg->avail_size > rchan->alloc_size) {
+ __set_current_state(TASK_INTERRUPTIBLE);
+ add_wait_queue(&ltt_buf->write_wait, &wait);
+ __raw_spin_unlock(&ltt_buf->lock);
+ local_irq_enable();
+ preempt_enable();
+ schedule();
+ __set_current_state(TASK_RUNNING);
+ remove_wait_queue(&ltt_buf->write_wait, &wait);
+ if (signal_pending(current))
+ return -ERESTARTSYS;
+ preempt_disable();
+ return 1;
+ }
+ }
+ __raw_spin_unlock(&ltt_buf->lock);
+ local_irq_enable();
+ return 0;
+}
+
+static void ltt_relay_print_user_errors(struct ltt_trace_struct *trace,
+ unsigned int chan_index, size_t data_size,
+ struct user_dbg_data *dbg, int cpu)
+{
+ struct rchan *rchan;
+ struct ltt_channel_buf_struct *ltt_buf;
+ struct ltt_channel_struct *channel;
+ struct rchan_buf *relay_buf;
+
+ channel = &trace->channels[chan_index];
+ rchan = channel->trans_channel_data;
+ relay_buf = rchan->buf[cpu];
+ ltt_buf = relay_buf->chan_private;
+
+ printk(KERN_ERR "Error in LTT usertrace : "
+ "buffer full : event lost in blocking "
+ "mode. Increase LTT_RESERVE_CRITICAL.\n");
+ printk(KERN_ERR "LTT nesting level is %u.\n",
+ per_cpu(ltt_nesting, cpu));
+ printk(KERN_ERR "LTT avail size %lu.\n",
+ dbg->avail_size);
+ printk(KERN_ERR "avai write : %lu, read : %lu\n",
+ dbg->write, dbg->read);
+
+ dbg->write = ltt_buf->offset;
+ dbg->read = ltt_buf->consumed;
+
+ printk(KERN_ERR "LTT cur size %lu.\n",
+ dbg->write + LTT_RESERVE_CRITICAL + data_size
+ - SUBBUF_TRUNC(dbg->read, relay_buf->chan));
+ printk(KERN_ERR "cur write : %lu, read : %lu\n",
+ dbg->write, dbg->read);
+}
+
+static struct ltt_transport ltt_relay_transport = {
+ .name = "relay-locked",
+ .owner = THIS_MODULE,
+ .ops = {
+ .create_dirs = ltt_relay_create_dirs,
+ .remove_dirs = ltt_relay_remove_dirs,
+ .create_channel = ltt_relay_create_channel,
+ .finish_channel = ltt_relay_finish_channel,
+ .remove_channel = ltt_relay_remove_channel,
+ .wakeup_channel = ltt_relay_async_wakeup_chan,
+ .commit_slot = ltt_relay_commit_slot,
+ .reserve_slot = ltt_relay_reserve_slot,
+ .user_blocking = ltt_relay_user_blocking,
+ .user_errors = ltt_relay_print_user_errors,
+ },
+};
+
+static const struct file_operations ltt_file_operations = {
+ .open = ltt_open,
+ .release = ltt_release,
+ .poll = ltt_poll,
+ .splice_read = ltt_relay_file_splice_read,
+ .ioctl = ltt_ioctl,
+#ifdef CONFIG_COMPAT
+ .compat_ioctl = ltt_compat_ioctl,
+#endif
+};
+
+static int __init ltt_relay_init(void)
+{
+ printk(KERN_INFO "LTT : ltt-relay-locked init\n");
+
+ ltt_transport_register(&ltt_relay_transport);
+
+ return 0;
+}
+
+static void __exit ltt_relay_exit(void)
+{
+ printk(KERN_INFO "LTT : ltt-relay-locked exit\n");
+
+ ltt_transport_unregister(&ltt_relay_transport);
+}
+
+module_init(ltt_relay_init);
+module_exit(ltt_relay_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Mathieu Desnoyers");
+MODULE_DESCRIPTION("Linux Trace Toolkit Next Generation Locked Relay");

--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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