ocfs2: Fix max offset calculations

ocfs2_max_file_offset() was over-estimating the largest file size for
several cases. This wasn't really a problem before, but now that we support
sparse files, it needs to be more accurate.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

1 files changed, 40 insertions, 28 deletions

diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
index a100b488533e..c3c89e26567c 100644
--- a/fs/ocfs2/super.c
+++ b/fs/ocfs2/super.c
@@ -316,39 +316,51 @@ static void ocfs2_destroy_inode(struct inode *inode)
         kmem_cache_free(ocfs2_inode_cachep, OCFS2_I(inode));
 }
 
-/* From xfs_super.c:xfs_max_file_offset
- * Copyright (c) 2000-2004 Silicon Graphics, Inc.
- */
-static unsigned long long ocfs2_max_file_offset(unsigned int blockshift)
+static unsigned long long ocfs2_max_file_offset(unsigned int bbits,
+                                                unsigned int cbits)
 {
-        unsigned int pagefactor = 1;
-        unsigned int bitshift = BITS_PER_LONG - 1;
-
-        /* Figure out maximum filesize, on Linux this can depend on
-         * the filesystem blocksize (on 32 bit platforms).
-         * __block_prepare_write does this in an [unsigned] long...
-         *      page->index << (PAGE_CACHE_SHIFT - bbits)
-         * So, for page sized blocks (4K on 32 bit platforms),
-         * this wraps at around 8Tb (hence MAX_LFS_FILESIZE which is
-         *      (((u64)PAGE_CACHE_SIZE << (BITS_PER_LONG-1))-1)
-         * but for smaller blocksizes it is less (bbits = log2 bsize).
-         * Note1: get_block_t takes a long (implicit cast from above)
-         * Note2: The Large Block Device (LBD and HAVE_SECTOR_T) patch
-         * can optionally convert the [unsigned] long from above into
-         * an [unsigned] long long.
+        unsigned int bytes = 1 << cbits;
+        unsigned int trim = bytes;
+        unsigned int bitshift = 32;
+
+        /*
+         * i_size and all block offsets in ocfs2 are always 64 bits
+         * wide. i_clusters is 32 bits, in cluster-sized units. So on
+         * 64 bit platforms, cluster size will be the limiting factor.
          */
 
 #if BITS_PER_LONG == 32
 # if defined(CONFIG_LBD)
         BUILD_BUG_ON(sizeof(sector_t) != 8);
-        pagefactor = PAGE_CACHE_SIZE;
-        bitshift = BITS_PER_LONG;
+        /*
+         * We might be limited by page cache size.
+         */
+        if (bytes > PAGE_CACHE_SIZE) {
+                bytes = PAGE_CACHE_SIZE;
+                trim = 1;
+                /*
+                 * Shift by 31 here so that we don't get larger than
+                 * MAX_LFS_FILESIZE
+                 */
+                bitshift = 31;
+        }
 # else
-        pagefactor = PAGE_CACHE_SIZE >> (PAGE_CACHE_SHIFT - blockshift);
+        /*
+         * We are limited by the size of sector_t. Use block size, as
+         * that's what we expose to the VFS.
+         */
+        bytes = 1 << bbits;
+        trim = 1;
+        bitshift = 31;
 # endif
 #endif
 
-        return (((unsigned long long)pagefactor) << bitshift) - 1;
+        /*
+         * Trim by a whole cluster when we can actually approach the
+         * on-disk limits. Otherwise we can overflow i_clusters when
+         * an extent start is at the max offset.
+         */
+        return (((unsigned long long)bytes) << bitshift) - trim;
 }
 
 static int ocfs2_remount(struct super_block *sb, int *flags, char *data)
@@ -1259,8 +1271,8 @@ static int ocfs2_initialize_super(struct super_block *sb,
                                   int sector_size)
 {
         int status = 0;
-        int i;
-        struct ocfs2_dinode *di = NULL;
+        int i, cbits, bbits;
+        struct ocfs2_dinode *di = (struct ocfs2_dinode *)bh->b_data;
         struct inode *inode = NULL;
         struct buffer_head *bitmap_bh = NULL;
         struct ocfs2_journal *journal;
@@ -1281,7 +1293,9 @@ static int ocfs2_initialize_super(struct super_block *sb,
         sb->s_export_op = &ocfs2_export_ops;
         sb->s_flags |= MS_NOATIME;
         /* this is needed to support O_LARGEFILE */
-        sb->s_maxbytes = ocfs2_max_file_offset(sb->s_blocksize_bits);
+        cbits = le32_to_cpu(di->id2.i_super.s_clustersize_bits);
+        bbits = le32_to_cpu(di->id2.i_super.s_blocksize_bits);
+        sb->s_maxbytes = ocfs2_max_file_offset(bbits, cbits);
 
         osb->sb = sb;
         /* Save off for ocfs2_rw_direct */
@@ -1341,8 +1355,6 @@ static int ocfs2_initialize_super(struct super_block *sb,
                 goto bail;
         }
 
-        di = (struct ocfs2_dinode *)bh->b_data;
-
         osb->max_slots = le16_to_cpu(di->id2.i_super.s_max_slots);
         if (osb->max_slots > OCFS2_MAX_SLOTS || osb->max_slots == 0) {
                 mlog(ML_ERROR, "Invalid number of node slots (%u)\n",