Re: [PATCH 05/11] fuse: Trust kernel i_mtime only -v2

From: Maxim Patlasov
Date: Thu Dec 26 2013 - 10:41:56 EST

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Hi Miklos,

Sorry for delay, see please inline comments below.

On 11/12/2013 08:52 PM, Miklos Szeredi wrote:

On Thu, Oct 10, 2013 at 05:10:56PM +0400, Maxim Patlasov wrote:
Let the kernel maintain i_mtime locally:
- clear S_NOCMTIME
- implement i_op->update_time()
- flush mtime on fsync and last close
- update i_mtime explicitly on truncate and fallocate

Fuse inode flag FUSE_I_MTIME_DIRTY serves as indication that local i_mtime
should be flushed to the server eventually.

Changed in v2 (thanks to Brian):
- renamed FUSE_I_MTIME_UPDATED to FUSE_I_MTIME_DIRTY
- simplified fuse_set_mtime_local()
- abandoned optimizations: clearing the flag on some operations (like
direct write) is doable, but may lead to unexpected changes of
user-visible mtime.

Signed-off-by: Maxim Patlasov <MPatlasov@xxxxxxxxxxxxx>
---
fs/fuse/dir.c | 109 ++++++++++++++++++++++++++++++++++++++++++++++++------
fs/fuse/file.c | 30 +++++++++++++--
fs/fuse/fuse_i.h | 6 ++-
fs/fuse/inode.c | 13 +++++-
4 files changed, 138 insertions(+), 20 deletions(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index f022968..eda248b 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -857,8 +857,11 @@ static void fuse_fillattr(struct inode *inode, struct fuse_attr *attr,
struct fuse_conn *fc = get_fuse_conn(inode);
/* see the comment in fuse_change_attributes() */
- if (fc->writeback_cache && S_ISREG(inode->i_mode))
+ if (fc->writeback_cache && S_ISREG(inode->i_mode)) {
attr->size = i_size_read(inode);
+ attr->mtime = inode->i_mtime.tv_sec;
+ attr->mtimensec = inode->i_mtime.tv_nsec;
+ }
stat->dev = inode->i_sb->s_dev;
stat->ino = attr->ino;
@@ -1582,6 +1585,82 @@ void fuse_release_nowrite(struct inode *inode)
spin_unlock(&fc->lock);
}
+static void fuse_setattr_fill(struct fuse_conn *fc, struct fuse_req *req,
+ struct inode *inode,
+ struct fuse_setattr_in *inarg_p,
+ struct fuse_attr_out *outarg_p)
+{
+ req->in.h.opcode = FUSE_SETATTR;
+ req->in.h.nodeid = get_node_id(inode);
+ req->in.numargs = 1;
+ req->in.args[0].size = sizeof(*inarg_p);
+ req->in.args[0].value = inarg_p;
+ req->out.numargs = 1;
+ if (fc->minor < 9)
+ req->out.args[0].size = FUSE_COMPAT_ATTR_OUT_SIZE;
+ else
+ req->out.args[0].size = sizeof(*outarg_p);
+ req->out.args[0].value = outarg_p;
+}
+
+/*
+ * Flush inode->i_mtime to the server
+ */
+int fuse_flush_mtime(struct file *file, bool nofail)
+{
+ struct inode *inode = file->f_mapping->host;
+ struct fuse_inode *fi = get_fuse_inode(inode);
+ struct fuse_conn *fc = get_fuse_conn(inode);
+ struct fuse_req *req = NULL;
+ struct fuse_setattr_in inarg;
+ struct fuse_attr_out outarg;
+ int err;
+
+ if (nofail) {
+ req = fuse_get_req_nofail_nopages(fc, file);
+ } else {
+ req = fuse_get_req_nopages(fc);
+ if (IS_ERR(req))
+ return PTR_ERR(req);
+ }
+
+ memset(&inarg, 0, sizeof(inarg));
+ memset(&outarg, 0, sizeof(outarg));
+
+ inarg.valid |= FATTR_MTIME;
+ inarg.mtime = inode->i_mtime.tv_sec;
+ inarg.mtimensec = inode->i_mtime.tv_nsec;
+
+ fuse_setattr_fill(fc, req, inode, &inarg, &outarg);
+ fuse_request_send(fc, req);
+ err = req->out.h.error;
+ fuse_put_request(fc, req);
+
+ if (!err)
+ clear_bit(FUSE_I_MTIME_DIRTY, &fi->state);
Doing the test and the clear separately opens a huge race window when i_mtime
modifications are bound to get lost.

No. Because the whole operation is protected by i_mutex (see fuse_fsync_common()).

+
+ return err;
+}
+
+/*
+ * S_NOCMTIME is clear, so we need to update inode->i_mtime manually.
+ */
+static void fuse_set_mtime_local(struct iattr *iattr, struct inode *inode)
+{
+ unsigned ivalid = iattr->ia_valid;
+ struct fuse_inode *fi = get_fuse_inode(inode);
+
+ if ((ivalid & ATTR_MTIME) && (ivalid & ATTR_MTIME_SET)) {
+ /* client fs has just set mtime to iattr->ia_mtime */
+ inode->i_mtime = iattr->ia_mtime;
+ clear_bit(FUSE_I_MTIME_DIRTY, &fi->state);

This is protected by i_mutex, so it should be safe.

Yes.

+ } else if ((ivalid & ATTR_MTIME) || (ivalid & ATTR_SIZE)) {
+ /* client fs doesn't know that we're updating i_mtime */

If so, why not tell the client fs to update mtime?

Looks reasonable. I'll resend updated patch soon.

+ inode->i_mtime = current_fs_time(inode->i_sb);
+ set_bit(FUSE_I_MTIME_DIRTY, &fi->state);
+ }
+}
+
/*
* Set attributes, and at the same time refresh them.
*
@@ -1641,17 +1720,7 @@ int fuse_do_setattr(struct inode *inode, struct iattr *attr,
inarg.valid |= FATTR_LOCKOWNER;
inarg.lock_owner = fuse_lock_owner_id(fc, current->files);
}
- req->in.h.opcode = FUSE_SETATTR;
- req->in.h.nodeid = get_node_id(inode);
- req->in.numargs = 1;
- req->in.args[0].size = sizeof(inarg);
- req->in.args[0].value = &inarg;
- req->out.numargs = 1;
- if (fc->minor < 9)
- req->out.args[0].size = FUSE_COMPAT_ATTR_OUT_SIZE;
- else
- req->out.args[0].size = sizeof(outarg);
- req->out.args[0].value = &outarg;
+ fuse_setattr_fill(fc, req, inode, &inarg, &outarg);
fuse_request_send(fc, req);
err = req->out.h.error;
fuse_put_request(fc, req);
@@ -1668,6 +1737,10 @@ int fuse_do_setattr(struct inode *inode, struct iattr *attr,
}
spin_lock(&fc->lock);
+ /* the kernel maintains i_mtime locally */
+ if (fc->writeback_cache && S_ISREG(inode->i_mode))
+ fuse_set_mtime_local(attr, inode);
+
fuse_change_attributes_common(inode, &outarg.attr,
attr_timeout(&outarg));
oldsize = inode->i_size;
@@ -1898,6 +1971,17 @@ static int fuse_removexattr(struct dentry *entry, const char *name)
return err;
}
+static int fuse_update_time(struct inode *inode, struct timespec *now,
+ int flags)
+{
+ if (flags & S_MTIME) {
+ inode->i_mtime = *now;
+ set_bit(FUSE_I_MTIME_DIRTY, &get_fuse_inode(inode)->state);
+ BUG_ON(!S_ISREG(inode->i_mode));
+ }
+ return 0;
+}
+
static const struct inode_operations fuse_dir_inode_operations = {
.lookup = fuse_lookup,
.mkdir = fuse_mkdir,
@@ -1937,6 +2021,7 @@ static const struct inode_operations fuse_common_inode_operations = {
.getxattr = fuse_getxattr,
.listxattr = fuse_listxattr,
.removexattr = fuse_removexattr,
+ .update_time = fuse_update_time,
};
static const struct inode_operations fuse_symlink_inode_operations = {
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 333a764..eabe202 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -291,6 +291,9 @@ static int fuse_open(struct inode *inode, struct file *file)
static int fuse_release(struct inode *inode, struct file *file)
{
+ if (test_bit(FUSE_I_MTIME_DIRTY, &get_fuse_inode(inode)->state))
So, why not make this test_and_clear_bit()?

To be uniform with fuse_fsync_common(). See please the next comment.

+ fuse_flush_mtime(file, true);
+
fuse_release_common(file, FUSE_RELEASE);
/* return value is ignored by VFS */
@@ -458,6 +461,12 @@ int fuse_fsync_common(struct file *file, loff_t start, loff_t end,
fuse_sync_writes(inode);
+ if (test_bit(FUSE_I_MTIME_DIRTY, &get_fuse_inode(inode)->state)) {
And this too.

If mtime flush fails, the bit is kept. Another way would be to use test_and_clear_bit() as you suggested, but set the bit back in case of failure. Technically they are equivalent (due to i_mutex protection), but current implementation looks more natural.

Thanks,
Maxim

+ int err = fuse_flush_mtime(file, false);
+ if (err)
+ goto out;
+ }
+
req = fuse_get_req_nopages(fc);
if (IS_ERR(req)) {
err = PTR_ERR(req);
@@ -948,16 +957,21 @@ static size_t fuse_send_write(struct fuse_req *req, struct fuse_io_priv *io,
return req->misc.write.out.size;
}
-void fuse_write_update_size(struct inode *inode, loff_t pos)
+bool fuse_write_update_size(struct inode *inode, loff_t pos)
{
struct fuse_conn *fc = get_fuse_conn(inode);
struct fuse_inode *fi = get_fuse_inode(inode);
+ bool ret = false;
spin_lock(&fc->lock);
fi->attr_version = ++fc->attr_version;
- if (pos > inode->i_size)
+ if (pos > inode->i_size) {
i_size_write(inode, pos);
+ ret = true;
+ }
spin_unlock(&fc->lock);
+
+ return ret;
}
static size_t fuse_send_write_pages(struct fuse_req *req, struct file *file,
@@ -2862,8 +2876,16 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
goto out;
/* we could have extended the file */
- if (!(mode & FALLOC_FL_KEEP_SIZE))
- fuse_write_update_size(inode, offset + length);
+ if (!(mode & FALLOC_FL_KEEP_SIZE)) {
+ bool changed = fuse_write_update_size(inode, offset + length);
+
+ if (changed && fc->writeback_cache) {
+ struct fuse_inode *fi = get_fuse_inode(inode);
+
+ inode->i_mtime = current_fs_time(inode->i_sb);
+ set_bit(FUSE_I_MTIME_DIRTY, &fi->state);
+ }
+ }
if (mode & FALLOC_FL_PUNCH_HOLE)
truncate_pagecache_range(inode, offset, offset + length - 1);
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index a490ba3..3028b8a 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -117,6 +117,8 @@ enum {
FUSE_I_ADVISE_RDPLUS,
/** An operation changing file size is in progress */
FUSE_I_SIZE_UNSTABLE,
+ /** i_mtime has been updated locally; a flush to userspace needed */
+ FUSE_I_MTIME_DIRTY,
};
struct fuse_conn;
@@ -870,7 +872,9 @@ long fuse_ioctl_common(struct file *file, unsigned int cmd,
unsigned fuse_file_poll(struct file *file, poll_table *wait);
int fuse_dev_release(struct inode *inode, struct file *file);
-void fuse_write_update_size(struct inode *inode, loff_t pos);
+bool fuse_write_update_size(struct inode *inode, loff_t pos);
+
+int fuse_flush_mtime(struct file *file, bool nofail);
int fuse_do_setattr(struct inode *inode, struct iattr *attr,
struct file *file);
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 63818ab..253701f 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -170,8 +170,11 @@ void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
inode->i_blocks = attr->blocks;
inode->i_atime.tv_sec = attr->atime;
inode->i_atime.tv_nsec = attr->atimensec;
- inode->i_mtime.tv_sec = attr->mtime;
- inode->i_mtime.tv_nsec = attr->mtimensec;
+ /* mtime from server may be stale due to local buffered write */
+ if (!fc->writeback_cache || !S_ISREG(inode->i_mode)) {
+ inode->i_mtime.tv_sec = attr->mtime;
+ inode->i_mtime.tv_nsec = attr->mtimensec;
+ }
inode->i_ctime.tv_sec = attr->ctime;
inode->i_ctime.tv_nsec = attr->ctimensec;
@@ -250,6 +253,8 @@ static void fuse_init_inode(struct inode *inode, struct fuse_attr *attr)
{
inode->i_mode = attr->mode & S_IFMT;
inode->i_size = attr->size;
+ inode->i_mtime.tv_sec = attr->mtime;
+ inode->i_mtime.tv_nsec = attr->mtimensec;
if (S_ISREG(inode->i_mode)) {
fuse_init_common(inode);
fuse_init_file_inode(inode);
@@ -296,7 +301,9 @@ struct inode *fuse_iget(struct super_block *sb, u64 nodeid,
return NULL;
if ((inode->i_state & I_NEW)) {
- inode->i_flags |= S_NOATIME|S_NOCMTIME;
+ inode->i_flags |= S_NOATIME;
+ if (!fc->writeback_cache)
+ inode->i_flags |= S_NOCMTIME;
inode->i_generation = generation;
inode->i_data.backing_dev_info = &fc->bdi;
fuse_init_inode(inode, attr);

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Next message: Maxim Patlasov: "[PATCH 05/11] fuse: Trust kernel i_mtime only -v3"
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