1 files changed, 61 insertions, 0 deletions

diff --git a/fs/file.c b/fs/file.c
index d8773b19fe47..f313314f996f 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -6,6 +6,7 @@
  *  Manage the dynamic fd arrays in the process files_struct.
  */
 
+#include <linux/module.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
 #include <linux/time.h>
@@ -432,3 +433,63 @@ struct files_struct init_files = {
         },
         .file_lock      = __SPIN_LOCK_UNLOCKED(init_task.file_lock),
 };
+
+/*
+ * allocate a file descriptor, mark it busy.
+ */
+int alloc_fd(unsigned start, unsigned flags)
+{
+        struct files_struct *files = current->files;
+        unsigned int fd;
+        int error;
+        struct fdtable *fdt;
+
+        spin_lock(&files->file_lock);
+repeat:
+        fdt = files_fdtable(files);
+        fd = start;
+        if (fd < files->next_fd)
+                fd = files->next_fd;
+
+        if (fd < fdt->max_fds)
+                fd = find_next_zero_bit(fdt->open_fds->fds_bits,
+                                           fdt->max_fds, fd);
+
+        error = expand_files(files, fd);
+        if (error < 0)
+                goto out;
+
+        /*
+         * If we needed to expand the fs array we
+         * might have blocked - try again.
+         */
+        if (error)
+                goto repeat;
+
+        if (start <= files->next_fd)
+                files->next_fd = fd + 1;
+
+        FD_SET(fd, fdt->open_fds);
+        if (flags & O_CLOEXEC)
+                FD_SET(fd, fdt->close_on_exec);
+        else
+                FD_CLR(fd, fdt->close_on_exec);
+        error = fd;
+#if 1
+        /* Sanity check */
+        if (rcu_dereference(fdt->fd[fd]) != NULL) {
+                printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
+                rcu_assign_pointer(fdt->fd[fd], NULL);
+        }
+#endif
+
+out:
+        spin_unlock(&files->file_lock);
+        return error;
+}
+
+int get_unused_fd(void)
+{
+        return alloc_fd(0, 0);
+}
+EXPORT_SYMBOL(get_unused_fd);