[PATCH v3 1/2] readdir: split the core of getdents64(2) out into vfs_getdents()

[Lennert Buytenhek]

So that IORING_OP_GETDENTS may use it, split out the core of the
getdents64(2) syscall into a helper function, vfs_getdents().

vfs_getdents() calls into filesystems' ->iterate{,_shared}() which
expect serialization on struct file, which means that callers of
vfs_getdents() are responsible for either using fdget_pos() or
performing the equivalent serialization by hand.

Cc: Al Viro <v...@zeniv.linux.org.uk>
Signed-off-by: Lennert Buytenhek <buyt...@wantstofly.org>
---
 fs/readdir.c       | 25 +++++++++++++++++--------
 include/linux/fs.h |  4 ++++
 2 files changed, 21 insertions(+), 8 deletions(-)

diff --git a/fs/readdir.c b/fs/readdir.c
index 19434b3c982c..f52167c1eb61 100644
--- a/fs/readdir.c
+++ b/fs/readdir.c
@@ -348,10 +348,9 @@ static int filldir64(struct dir_context *ctx, const char 
*name, int namlen,
        return -EFAULT;
 }
 
-SYSCALL_DEFINE3(getdents64, unsigned int, fd,
-               struct linux_dirent64 __user *, dirent, unsigned int, count)
+int vfs_getdents(struct file *file, struct linux_dirent64 __user *dirent,
+                unsigned int count)
 {
-       struct fd f;
        struct getdents_callback64 buf = {
                .ctx.actor = filldir64,
                .count = count,
@@ -359,11 +358,7 @@ SYSCALL_DEFINE3(getdents64, unsigned int, fd,
        };
        int error;
 
-       f = fdget_pos(fd);
-       if (!f.file)
-               return -EBADF;
-
-       error = iterate_dir(f.file, &buf.ctx);
+       error = iterate_dir(file, &buf.ctx);
        if (error >= 0)
                error = buf.error;
        if (buf.prev_reclen) {
@@ -376,6 +371,20 @@ SYSCALL_DEFINE3(getdents64, unsigned int, fd,
                else
                        error = count - buf.count;
        }
+       return error;
+}
+
+SYSCALL_DEFINE3(getdents64, unsigned int, fd,
+               struct linux_dirent64 __user *, dirent, unsigned int, count)
+{
+       struct fd f;
+       int error;
+
+       f = fdget_pos(fd);
+       if (!f.file)
+               return -EBADF;
+
+       error = vfs_getdents(f.file, dirent, count);
        fdput_pos(f);
        return error;
 }
diff --git a/include/linux/fs.h b/include/linux/fs.h
index fd47deea7c17..114885d3f6c4 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3109,6 +3109,10 @@ extern const struct inode_operations 
simple_symlink_inode_operations;
 
 extern int iterate_dir(struct file *, struct dir_context *);
 
+struct linux_dirent64;
+int vfs_getdents(struct file *file, struct linux_dirent64 __user *dirent,
+                unsigned int count);
+
 int vfs_fstatat(int dfd, const char __user *filename, struct kstat *stat,
                int flags);
 int vfs_fstat(int fd, struct kstat *stat);
-- 
2.29.2