[PATCH] Fix page cache limit wrapping in filesystems

Several file systems in tree that nominally support files >2GB set their
s_maxbytes value to ~0ULL. This has the nasty side effect on 32bit machines
that when a file write reaches the page cache limit (e.g. 2^43) it'll silently
wrap and destroy data at the beginning of the file.

This patch changes the file systems in question to fill in a proper limit.

I also have an alternate patch that adds a check for this generically
in super.c, but preliminary comments from Al suggested that he prefered
to do it in the file systems, so it is done this way way.

fs/nfs/inode.c

@@ -455,6 +455,8 @@ nfs_read_super(struct super_block *sb, void *raw_data, int silent)
                 server->namelen = maxlen;
 
 	sb->s_maxbytes = fsinfo.maxfilesize;
+	if (sb->s_maxbytes > MAX_LFS_FILESIZE) 
+		sb->s_maxbytes = MAX_LFS_FILESIZE; 
 
 	/* Fire up the writeback cache */
 	if (nfs_reqlist_alloc(server) < 0) {

fs/ntfs/fs.c

@@ -1130,7 +1130,7 @@ struct super_block *ntfs_read_super(struct super_block *sb, void *options,
 	/* Inform the kernel about which super operations are available. */
 	sb->s_op = &ntfs_super_operations;
 	sb->s_magic = NTFS_SUPER_MAGIC;
-	sb->s_maxbytes = ~0ULL >> 1;
+	sb->s_maxbytes = MAX_LFS_FILESIZE;
 	ntfs_debug(DEBUG_OTHER, "Reading special files\n");
 	if (ntfs_load_special_files(vol)) {
 		ntfs_error("Error loading special files\n");

fs/udf/super.c

@@ -1544,7 +1544,7 @@ udf_read_super(struct super_block *sb, void *options, int silent)
 		iput(inode);
 		goto error_out;
 	}
-	sb->s_maxbytes = ~0ULL;
+	sb->s_maxbytes = MAX_LFS_FILESIZE;
 	return sb;
 
 error_out:

include/linux/fs.h

@@ -520,6 +520,14 @@ extern int init_private_file(struct file *, struct dentry *, int);
 
 #define	MAX_NON_LFS	((1UL<<31) - 1)
 
+/* Page cache limit. The filesystems should put that into their s_maxbytes 
+   limits, otherwise bad things can happen in VM. */ 
+#if BITS_PER_LONG==32
+#define MAX_LFS_FILESIZE	(((u64)PAGE_CACHE_SIZE << (BITS_PER_LONG-1))-1) 
+#elif BITS_PER_LONG==64
+#define MAX_LFS_FILESIZE 	0x7fffffffffffffff
+#endif
+
 #define FL_POSIX	1
 #define FL_FLOCK	2
 #define FL_BROKEN	4	/* broken flock() emulation */