[PATCH] fs: add FD_CLOFORK and O_CLOFORK

From: Changli Gao
Date: Sat May 07 2011 - 00:50:29 EST

If FD_CLOFORK is 1, when a fork occurs, the corresponding file descriptor
will be closed for the child process. IOW, the file descriptor isn't
inheritable.

FD_CLOFORK is used as IBM does.

O_CLOFORK is also added to avoid the additional fcntl(2) after open(2).

Signed-off-by: Changli Gao <xiaosuo@xxxxxxxxx>
---
fs/fcntl.c | 27 +++++++++++++++++++++++++++
fs/file.c | 22 ++++++++++++++++++++--
include/asm-generic/fcntl.h | 5 +++++
include/linux/fdtable.h | 2 ++
include/linux/file.h | 1 +
5 files changed, 55 insertions(+), 2 deletions(-)
diff --git a/fs/fcntl.c b/fs/fcntl.c
index 22764c7..8127744 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -50,6 +50,31 @@ static int get_close_on_exec(unsigned int fd)
return res;
}

+void set_close_on_fork(unsigned int fd, int flag)
+{
+ struct files_struct *files = current->files;
+ struct fdtable *fdt;
+ spin_lock(&files->file_lock);
+ fdt = files_fdtable(files);
+ if (flag)
+ FD_SET(fd, fdt->close_on_fork);
+ else
+ FD_CLR(fd, fdt->close_on_fork);
+ spin_unlock(&files->file_lock);
+}
+
+static int get_close_on_fork(unsigned int fd)
+{
+ struct files_struct *files = current->files;
+ struct fdtable *fdt;
+ int res;
+ rcu_read_lock();
+ fdt = files_fdtable(files);
+ res = FD_ISSET(fd, fdt->close_on_fork);
+ rcu_read_unlock();
+ return res;
+}
+
SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags)
{
int err = -EBADF;
@@ -358,10 +383,12 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
break;
case F_GETFD:
err = get_close_on_exec(fd) ? FD_CLOEXEC : 0;
+ err |= get_close_on_fork(fd) ? FD_CLOFORK : 0;
break;
case F_SETFD:
err = 0;
set_close_on_exec(fd, arg & FD_CLOEXEC);
+ set_close_on_fork(fd, arg & FD_CLOFORK);
break;
case F_GETFL:
err = filp->f_flags;
diff --git a/fs/file.c b/fs/file.c
index 0be3447..ef79197 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -133,6 +133,8 @@ static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
memset((char *)(nfdt->open_fds) + cpy, 0, set);
memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy);
memset((char *)(nfdt->close_on_exec) + cpy, 0, set);
+ memcpy(nfdt->close_on_fork, ofdt->close_on_fork, cpy);
+ memset((char *)(nfdt->close_on_fork) + cpy, 0, set);
}

static struct fdtable * alloc_fdtable(unsigned int nr)
@@ -170,12 +172,14 @@ static struct fdtable * alloc_fdtable(unsigned int nr)
goto out_fdt;
fdt->fd = (struct file **)data;
data = alloc_fdmem(max_t(unsigned int,
- 2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
+ 3 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
if (!data)
goto out_arr;
fdt->open_fds = (fd_set *)data;
data += nr / BITS_PER_BYTE;
fdt->close_on_exec = (fd_set *)data;
+ data += nr / BITS_PER_BYTE;
+ fdt->close_on_fork = (fd_set *)data;
fdt->next = NULL;

return fdt;
@@ -303,6 +307,7 @@ struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
new_fdt = &newf->fdtab;
new_fdt->max_fds = NR_OPEN_DEFAULT;
new_fdt->close_on_exec = (fd_set *)&newf->close_on_exec_init;
+ new_fdt->close_on_fork = (fd_set *)&newf->close_on_fork_init;
new_fdt->open_fds = (fd_set *)&newf->open_fds_init;
new_fdt->fd = &newf->fd_array[0];
new_fdt->next = NULL;
@@ -350,11 +355,18 @@ struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
old_fdt->open_fds->fds_bits, open_files/8);
memcpy(new_fdt->close_on_exec->fds_bits,
old_fdt->close_on_exec->fds_bits, open_files/8);
+ memcpy(new_fdt->close_on_fork->fds_bits,
+ old_fdt->close_on_fork->fds_bits, open_files/8);

for (i = open_files; i != 0; i--) {
struct file *f = *old_fds++;
if (f) {
- get_file(f);
+ if (FD_ISSET(open_files - i, new_fdt->close_on_fork)) {
+ FD_CLR(open_files - i, new_fdt->open_fds);
+ f = NULL;
+ } else {
+ get_file(f);
+ }
} else {
/*
* The fd may be claimed in the fd bitmap but not yet
@@ -380,6 +392,7 @@ struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)

memset(&new_fdt->open_fds->fds_bits[start], 0, left);
memset(&new_fdt->close_on_exec->fds_bits[start], 0, left);
+ memset(&new_fdt->close_on_fork->fds_bits[start], 0, left);
}

rcu_assign_pointer(newf->fdt, new_fdt);
@@ -416,6 +429,7 @@ struct files_struct init_files = {
.max_fds = NR_OPEN_DEFAULT,
.fd = &init_files.fd_array[0],
.close_on_exec = (fd_set *)&init_files.close_on_exec_init,
+ .close_on_fork = (fd_set *)&init_files.close_on_fork_init,
.open_fds = (fd_set *)&init_files.open_fds_init,
},
.file_lock = __SPIN_LOCK_UNLOCKED(init_task.file_lock),
@@ -461,6 +475,10 @@ repeat:
FD_SET(fd, fdt->close_on_exec);
else
FD_CLR(fd, fdt->close_on_exec);
+ if (flags & O_CLOFORK)
+ FD_SET(fd, fdt->close_on_fork);
+ else
+ FD_CLR(fd, fdt->close_on_fork);
error = fd;
#if 1
/* Sanity check */
diff --git a/include/asm-generic/fcntl.h b/include/asm-generic/fcntl.h
index 84793c7..2a7c474 100644
--- a/include/asm-generic/fcntl.h
+++ b/include/asm-generic/fcntl.h
@@ -88,6 +88,10 @@
#define O_NDELAY O_NONBLOCK
#endif

+#ifndef O_CLOFORK
+#define O_CLOFORK 020000000 /* set close_on_fork */
+#endif
+
#define F_DUPFD 0 /* dup */
#define F_GETFD 1 /* get close_on_exec */
#define F_SETFD 2 /* set/clear close_on_exec */
@@ -131,6 +135,7 @@ struct f_owner_ex {

/* for F_[GET|SET]FL */
#define FD_CLOEXEC 1 /* actually anything with low bit set goes */
+#define FD_CLOFORK 2

/* for posix fcntl() and lockf() */
#ifndef F_RDLCK
diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index 133c0ba..bb9f0be 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -33,6 +33,7 @@ struct fdtable {
unsigned int max_fds;
struct file __rcu **fd; /* current fd array */
fd_set *close_on_exec;
+ fd_set *close_on_fork;
fd_set *open_fds;
struct rcu_head rcu;
struct fdtable *next;
@@ -54,6 +55,7 @@ struct files_struct {
spinlock_t file_lock ____cacheline_aligned_in_smp;
int next_fd;
struct embedded_fd_set close_on_exec_init;
+ struct embedded_fd_set close_on_fork_init;
struct embedded_fd_set open_fds_init;
struct file __rcu * fd_array[NR_OPEN_DEFAULT];
};
diff --git a/include/linux/file.h b/include/linux/file.h
index 21a7995..c592d1f 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -32,6 +32,7 @@ extern struct file *fget_light(unsigned int fd, int *fput_needed);
extern struct file *fget_raw(unsigned int fd);
extern struct file *fget_raw_light(unsigned int fd, int *fput_needed);
extern void set_close_on_exec(unsigned int fd, int flag);
+extern void set_close_on_fork(unsigned int fd, int flag);
extern void put_filp(struct file *);
extern int alloc_fd(unsigned start, unsigned flags);
extern int get_unused_fd(void);
--
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