[PATCH] reiserfs: Remove 2 TB file size limit

[Jeff Mahoney <jeffm@suse.com>]

 In its early life, reiserfs had an evolving s_max_bytes. It started out
 at 4 GB, then was raised to MAX_LFS_FILESIZE, then dropped to 2 TiB when
 it was observed that struct stat only had a 32-bit st_blocks field.

 Since then, both the kernel and glibc have evolved as well and now both
 support 64-bit st_blocks. Applications that can't deal with these ranges
 are assumed to be "legacy" or "broken." File systems now routinely
 support file sizes much larger than can be represented by 2^32 * 512.

 But we never revisited that limitation. ReiserFS has always been able to
 support larger file sizes (up to 16 TiB, in fact), but the s_max_bytes
 limitation has prevented that.

 This patch adds a max_file_offset helper to set s_max_bytes to a more
 appropriate value. I noticed that XFS adjusts the limit based on the
 CPU but I'd prefer to err on the side of compatibility and place the
 limit at the smaller of the 32-bit MAX_LFS_FILESIZE and the maximum
 supported by the file system. At a 4k block size, this is conveniently
 also the advertised maximum file size of reiserfs.

 This bug is tracked at: https://bugzilla.novell.com/show_bug.cgi?id=592100

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
---
 fs/reiserfs/super.c |   17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

--- a/fs/reiserfs/super.c
+++ b/fs/reiserfs/super.c
@@ -1309,6 +1309,18 @@ out_err:
 	return err;
 }
 
+static inline loff_t
+reiserfs_max_file_offset(struct super_block *sb)
+{
+	/* Limited by stat_data->sd_blocks, 2^32-1 blocks */
+	loff_t fs_max = (sb->s_blocksize << 32) - sb->s_blocksize;
+
+	/* Limited by 32-bit MAX_LFS_FILESIZE */
+	loff_t page_cache_max = (((u64)PAGE_CACHE_SIZE << 31)-1);
+
+	return min(fs_max, page_cache_max);
+}
+
 static int read_super_block(struct super_block *s, int offset)
 {
 	struct buffer_head *bh;
@@ -1398,10 +1410,7 @@ static int read_super_block(struct super
 	s->dq_op = &reiserfs_quota_operations;
 #endif
 
-	/* new format is limited by the 32 bit wide i_blocks field, want to
-	 ** be one full block below that.
-	 */
-	s->s_maxbytes = (512LL << 32) - s->s_blocksize;
+	s->s_maxbytes = reiserfs_max_file_offset(s);
 	return 0;
 }