vfs: change sb->s_maxbytes to a loff_t

sb->s_maxbytes is supposed to indicate the maximum size of a file that can
exist on the filesystem.  It's declared as an unsigned long long.

Even if a filesystem has no inherent limit that prevents it from using
every bit in that unsigned long long, it's still problematic to set it to
anything larger than MAX_LFS_FILESIZE.  There are places in the kernel
that cast s_maxbytes to a signed value.  If it's set too large then this
cast makes it a negative number and generally breaks the comparison.

Change s_maxbytes to be loff_t instead.  That should help eliminate the
temptation to set it too large by making it a signed value.

Also, add a warning for couple of releases to help catch filesystems that
set s_maxbytes too large.  Eventually we can either convert this to a
BUG() or just remove it and in the hope that no one will get it wrong now
that it's a signed value.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Robert Love <rlove@google.com>
Cc: Mandeep Singh Baines <msb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 955e34615cb7..cbb7724c11d3 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1315,7 +1315,7 @@ struct super_block {
         unsigned long           s_blocksize;
         unsigned char           s_blocksize_bits;
         unsigned char           s_dirt;
-        unsigned long long      s_maxbytes;     /* Max file size */
+        loff_t                  s_maxbytes;     /* Max file size */
         struct file_system_type *s_type;
         const struct super_operations   *s_op;
         const struct dquot_operations   *dq_op;