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>

3 files changed, 16 insertions, 58 deletions

diff --git a/drivers/staging/android/binder.c b/drivers/staging/android/binder.c
index b9a534c46aac..4946d282a35c 100644
--- a/drivers/staging/android/binder.c
+++ b/drivers/staging/android/binder.c
@@ -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);
 }
 
 /*
diff --git a/fs/file.c b/fs/file.c
index 08922af4a62c..a3a0705f8f51 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -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 @@ out:
         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);
diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index 158a41eed314..b84ca064f727 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -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 */