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Wrap accesses to the fd_sets in struct fdtable

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Wrap accesses to the fd_sets in struct fdtable (for recording open files and
close-on-exec flags) so that we can move away from using fd_sets since we
abuse the fd_set structs by not allocating the full-sized structure under
normal circumstances and by non-core code looking at the internals of the
fd_sets.

The first abuse means that use of FD_ZERO() on these fd_sets is not permitted,
since that cannot be told about their abnormal lengths.

This introduces six wrapper functions for setting, clearing and testing
close-on-exec flags and fd-is-open flags:

	void __set_close_on_exec(int fd, struct fdtable *fdt);
	void __clear_close_on_exec(int fd, struct fdtable *fdt);
	bool close_on_exec(int fd, const struct fdtable *fdt);
	void __set_open_fd(int fd, struct fdtable *fdt);
	void __clear_open_fd(int fd, struct fdtable *fdt);
	bool fd_is_open(int fd, const struct fdtable *fdt);

Note that I've prepended '__' to the names of the set/clear functions because
they require the caller to hold a lock to use them.

Note also that I haven't added wrappers for looking behind the scenes at the
the array.  Possibly that should exist too.

Signed-off-by: David Howells <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: H. Peter Anvin <[email protected]>
Cc: Al Viro <[email protected]>
This commit is contained in:
David Howells 2012-02-16 17:49:42 +00:00 • committed by H. Peter Anvin
commit 1dce27c5aa
10 changed files with 57 additions and 27 deletions
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18
fs/fcntl.c
View file

@ -32,20 +32,20 @@ void set_close_on_exec(unsigned int fd, int flag)
spin_lock(&files->file_lock);
fdt = files_fdtable(files);
if (flag)
FD_SET(fd, fdt->close_on_exec);
__set_close_on_exec(fd, fdt);
else
FD_CLR(fd, fdt->close_on_exec);
__clear_close_on_exec(fd, fdt);
spin_unlock(&files->file_lock);
}
static int get_close_on_exec(unsigned int fd)
static bool get_close_on_exec(unsigned int fd)
{
struct files_struct *files = current->files;
struct fdtable *fdt;
int res;
bool res;
rcu_read_lock();
fdt = files_fdtable(files);
res = FD_ISSET(fd, fdt->close_on_exec);
res = close_on_exec(fd, fdt);
rcu_read_unlock();
return res;
}
@ -90,15 +90,15 @@ SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags)
err = -EBUSY;
fdt = files_fdtable(files);
tofree = fdt->fd[newfd];
if (!tofree && FD_ISSET(newfd, fdt->open_fds))
if (!tofree && fd_is_open(newfd, fdt))
goto out_unlock;
get_file(file);
rcu_assign_pointer(fdt->fd[newfd], file);
FD_SET(newfd, fdt->open_fds);
__set_open_fd(newfd, fdt);
if (flags & O_CLOEXEC)
FD_SET(newfd, fdt->close_on_exec);
__set_close_on_exec(newfd, fdt);
else
FD_CLR(newfd, fdt->close_on_exec);
__clear_close_on_exec(newfd, fdt);
spin_unlock(&files->file_lock);
if (tofree)