The ffs superblock includes a 128-byte region for use by temporary

in-core pointers to summary information. An array in this region
(fs_csp) could overflow on filesystems with a very large number of
cylinder groups (~16000 on i386 with 8k blocks). When this happens,
other fields in the superblock get corrupted, and fsck refuses to
check the filesystem.

Solve this problem by replacing the fs_csp array in 'struct fs'
with a single pointer, and add padding to keep the length of the
128-byte region fixed. Update the kernel and userland utilities
to use just this single pointer.

With this change, the kernel no longer makes use of the superblock
fields 'fs_csshift' and 'fs_csmask'. Add a comment to newfs/mkfs.c
to indicate that these fields must be calculated for compatibility
with older kernels.

Reviewed by:	mckusick

1 files changed, 5 insertions, 0 deletions

diff --git a/sbin/newfs/mkfs.c b/sbin/newfs/mkfs.c
index 7e5ea14..4cf854b 100644
--- a/sbin/newfs/mkfs.c
+++ b/sbin/newfs/mkfs.c
@@ -633,6 +633,11 @@ next:
 	sblock.fs_csaddr = cgdmin(&sblock, 0);
 	sblock.fs_cssize =
 	    fragroundup(&sblock, sblock.fs_ncg * sizeof(struct csum));
+	/*
+	 * The superblock fields 'fs_csmask' and 'fs_csshift' are no
+	 * longer used. However, we still initialise them so that the
+	 * filesystem remains compatible with old kernels.
+	 */
 	i = sblock.fs_bsize / sizeof(struct csum);
 	sblock.fs_csmask = ~(i - 1);
 	for (sblock.fs_csshift = 0; i > 1; i >>= 1)