[PATCH] sys_sync_file_range()

Remove the recently-added LINUX_FADV_ASYNC_WRITE and LINUX_FADV_WRITE_WAIT
fadvise() additions, do it in a new sys_sync_file_range() syscall instead.
Reasons:

- It's more flexible.  Things which would require two or three syscalls with
  fadvise() can be done in a single syscall.

- Using fadvise() in this manner is something not covered by POSIX.

The patch wires up the syscall for x86.

The sycall is implemented in the new fs/sync.c.  The intention is that we can
move sys_fsync(), sys_fdatasync() and perhaps sys_sync() into there later.

Documentation for the syscall is in fs/sync.c.

A test app (sync_file_range.c) is in
http://www.zip.com.au/~akpm/linux/patches/stuff/ext3-tools.tar.gz.

The available-to-GPL-modules do_sync_file_range() is for knfsd: "A COMMIT can
say NFS_DATA_SYNC or NFS_FILE_SYNC.  I can skip the ->fsync call for
NFS_DATA_SYNC which is hopefully the more common."

Note: the `async' writeout mode SYNC_FILE_RANGE_WRITE will turn synchronous if
the queue is congested.  This is trivial to fix: add a new flag bit, set
wbc->nonblocking.  But I'm not sure that we want to expose implementation
details down to that level.

Note: it's notable that we can sync an fd which wasn't opened for writing.
Same with fsync() and fdatasync()).

Note: the code takes some care to handle attempts to sync file contents
outside the 16TB offset on 32-bit machines.  It makes such attempts appear to
succeed, for best 32-bit/64-bit compatibility.  Perhaps it should make such
requests fail...

Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 9 insertions, 6 deletions

diff --git a/include/linux/fadvise.h b/include/linux/fadvise.h
index b2913bba35d8..e8e747139b9a 100644
--- a/include/linux/fadvise.h
+++ b/include/linux/fadvise.h
@@ -18,10 +18,4 @@
 #define POSIX_FADV_NOREUSE      5 /* Data will be accessed once.  */
 #endif
 
-/*
- * Linux-specific fadvise() extensions:
- */
-#define LINUX_FADV_ASYNC_WRITE  32      /* Start writeout on range */
-#define LINUX_FADV_WRITE_WAIT   33      /* Wait upon writeout to range */
-
 #endif  /* FADVISE_H_INCLUDED */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 20a7afd4590c..4ed7e602d703 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -757,6 +757,13 @@ extern void send_sigio(struct fown_struct *fown, int fd, int band);
 extern int fcntl_setlease(unsigned int fd, struct file *filp, long arg);
 extern int fcntl_getlease(struct file *filp);
 
+/* fs/sync.c */
+#define SYNC_FILE_RANGE_WAIT_BEFORE     1
+#define SYNC_FILE_RANGE_WRITE           2
+#define SYNC_FILE_RANGE_WAIT_AFTER      4
+extern int do_sync_file_range(struct file *file, loff_t offset, loff_t endbyte,
+                        int flags);
+
 /* fs/locks.c */
 extern void locks_init_lock(struct file_lock *);
 extern void locks_copy_lock(struct file_lock *, struct file_lock *);
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index e78ffc7d5b56..5717147596b6 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -571,5 +571,7 @@ asmlinkage long compat_sys_openat(unsigned int dfd, const char __user *filename,
 asmlinkage long sys_unshare(unsigned long unshare_flags);
 asmlinkage long sys_splice(int fdin, int fdout, size_t len,
                                 unsigned int flags);
+asmlinkage long sys_sync_file_range(int fd, loff_t offset, loff_t nbytes,
+                                        int flags);
 
 #endif