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new helper: __alloc_fd()

Essentially, alloc_fd() in a files_struct we own a reference to.
Most of the time wanting to use it is a sign of lousy API
design (such as android/binder).  It's *not* a general-purpose
interface; better that than open-coding its guts, but again,
playing with other process' descriptor table is a sign of bad
design.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Al Viro
Al Viro committed Aug 12, 2012
1 parent f33ff99 commit dcfadfa4ec5a12404a99ad6426871a6b03a62b37
Showing with 16 additions and 58 deletions.
  1. +5 −54 drivers/staging/android/binder.c
  2. +8 −4 fs/file.c
  3. +3 −0 include/linux/fdtable.h
@@ -362,71 +362,22 @@ struct binder_transaction {
static void
binder_defer_work(struct binder_proc *proc, enum binder_deferred_state defer);
/*
* copied from get_unused_fd_flags
*/
int task_get_unused_fd_flags(struct binder_proc *proc, int flags)
{
struct files_struct *files = proc->files;
int fd, error;
struct fdtable *fdt;
unsigned long rlim_cur;
unsigned long irqs;
if (files == NULL)
return -ESRCH;
error = -EMFILE;
spin_lock(&files->file_lock);
if (!lock_task_sighand(proc->tsk, &irqs))
return -EMFILE;
repeat:
fdt = files_fdtable(files);
fd = find_next_zero_bit(fdt->open_fds, fdt->max_fds, files->next_fd);
/*
* N.B. For clone tasks sharing a files structure, this test
* will limit the total number of files that can be opened.
*/
rlim_cur = 0;
if (lock_task_sighand(proc->tsk, &irqs)) {
rlim_cur = proc->tsk->signal->rlim[RLIMIT_NOFILE].rlim_cur;
unlock_task_sighand(proc->tsk, &irqs);
}
if (fd >= rlim_cur)
goto out;
/* Do we need to expand the fd array or fd set? */
error = expand_files(files, fd);
if (error < 0)
goto out;
if (error) {
/*
* If we needed to expand the fs array we
* might have blocked - try again.
*/
error = -EMFILE;
goto repeat;
}
__set_open_fd(fd, fdt);
if (flags & O_CLOEXEC)
__set_close_on_exec(fd, fdt);
else
__clear_close_on_exec(fd, fdt);
files->next_fd = fd + 1;
#if 1
/* Sanity check */
if (fdt->fd[fd] != NULL) {
pr_warn("get_unused_fd: slot %d not NULL!\n", fd);
fdt->fd[fd] = NULL;
}
#endif
error = fd;
rlim_cur = task_rlimit(proc->tsk, RLIMIT_NOFILE);
unlock_task_sighand(proc->tsk, &irqs);
out:
spin_unlock(&files->file_lock);
return error;
return __alloc_fd(files, 0, rlim_cur, flags);
}
/*
@@ -420,11 +420,10 @@ struct files_struct init_files = {
/*
* allocate a file descriptor, mark it busy.
*/
int alloc_fd(unsigned start, unsigned flags)
int __alloc_fd(struct files_struct *files,
unsigned start, unsigned end, unsigned flags)
{
struct files_struct *files = current->files;
unsigned int fd;
unsigned end = rlimit(RLIMIT_NOFILE);
int error;
struct fdtable *fdt;
@@ -479,8 +478,13 @@ int alloc_fd(unsigned start, unsigned flags)
return error;
}
int alloc_fd(unsigned start, unsigned flags)
{
return __alloc_fd(current->files, start, rlimit(RLIMIT_NOFILE), flags);
}
int get_unused_fd_flags(unsigned flags)
{
return alloc_fd(0, flags);
return __alloc_fd(current->files, 0, rlimit(RLIMIT_NOFILE), flags);
}
EXPORT_SYMBOL(get_unused_fd_flags);
@@ -125,6 +125,9 @@ void reset_files_struct(struct files_struct *);
int unshare_files(struct files_struct **);
struct files_struct *dup_fd(struct files_struct *, int *);
extern int __alloc_fd(struct files_struct *files,
unsigned start, unsigned end, unsigned flags);
extern struct kmem_cache *files_cachep;
#endif /* __LINUX_FDTABLE_H */

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