new helper: replace_fd()

analog of dup2(), except that it takes struct file * as source.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 62 insertions, 29 deletions

diff --git a/fs/file.c b/fs/file.c
index 7f29544755d0..a7bbe0324478 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -821,29 +821,12 @@ bool get_close_on_exec(unsigned int fd)
         return res;
 }
 
-SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags)
+static int do_dup2(struct files_struct *files,
+        struct file *file, unsigned fd, unsigned flags)
 {
-        int err = -EBADF;
-        struct file * file, *tofree;
-        struct files_struct * files = current->files;
+        struct file *tofree;
         struct fdtable *fdt;
 
-        if ((flags & ~O_CLOEXEC) != 0)
-                return -EINVAL;
-
-        if (newfd >= rlimit(RLIMIT_NOFILE))
-                return -EMFILE;
-
-        spin_lock(&files->file_lock);
-        err = expand_files(files, newfd);
-        file = fcheck(oldfd);
-        if (unlikely(!file))
-                goto Ebadf;
-        if (unlikely(err < 0)) {
-                if (err == -EMFILE)
-                        goto Ebadf;
-                goto out_unlock;
-        }
         /*
          * We need to detect attempts to do dup2() over allocated but still
          * not finished descriptor.  NB: OpenBSD avoids that at the price of
@@ -858,24 +841,74 @@ SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags)
          * scope of POSIX or SUS, since neither considers shared descriptor
          * tables and this condition does not arise without those.
          */
-        err = -EBUSY;
         fdt = files_fdtable(files);
-        tofree = fdt->fd[newfd];
-        if (!tofree && fd_is_open(newfd, fdt))
-                goto out_unlock;
+        tofree = fdt->fd[fd];
+        if (!tofree && fd_is_open(fd, fdt))
+                goto Ebusy;
         get_file(file);
-        rcu_assign_pointer(fdt->fd[newfd], file);
-        __set_open_fd(newfd, fdt);
+        rcu_assign_pointer(fdt->fd[fd], file);
+        __set_open_fd(fd, fdt);
         if (flags & O_CLOEXEC)
-                __set_close_on_exec(newfd, fdt);
+                __set_close_on_exec(fd, fdt);
         else
-                __clear_close_on_exec(newfd, fdt);
+                __clear_close_on_exec(fd, fdt);
         spin_unlock(&files->file_lock);
 
         if (tofree)
                 filp_close(tofree, files);
 
-        return newfd;
+        return fd;
+
+Ebusy:
+        spin_unlock(&files->file_lock);
+        return -EBUSY;
+}
+
+int replace_fd(unsigned fd, struct file *file, unsigned flags)
+{
+        int err;
+        struct files_struct *files = current->files;
+
+        if (!file)
+                return __close_fd(files, fd);
+
+        if (fd >= rlimit(RLIMIT_NOFILE))
+                return -EMFILE;
+
+        spin_lock(&files->file_lock);
+        err = expand_files(files, fd);
+        if (unlikely(err < 0))
+                goto out_unlock;
+        return do_dup2(files, file, fd, flags);
+
+out_unlock:
+        spin_unlock(&files->file_lock);
+        return err;
+}
+
+SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags)
+{
+        int err = -EBADF;
+        struct file *file;
+        struct files_struct *files = current->files;
+
+        if ((flags & ~O_CLOEXEC) != 0)
+                return -EINVAL;
+
+        if (newfd >= rlimit(RLIMIT_NOFILE))
+                return -EMFILE;
+
+        spin_lock(&files->file_lock);
+        err = expand_files(files, newfd);
+        file = fcheck(oldfd);
+        if (unlikely(!file))
+                goto Ebadf;
+        if (unlikely(err < 0)) {
+                if (err == -EMFILE)
+                        goto Ebadf;
+                goto out_unlock;
+        }
+        return do_dup2(files, file, newfd, flags);
 
 Ebadf:
         err = -EBADF;