Linux bug mounting FreeBSD partitions

[comet--berkeley]

My MBR formatted disk drive has Linux, OpenBSD and FreeBSD in separate partitions.

When Linux starts up and tries to recognize FreeBSD subpartitions, it always fails with this message:

sda3: <bsd:bad subpartition - ignored ...

Linux has no trouble with the OpenBSD subpartitions:

sda2: <openbsd: sda16 sda17 sda18 ...

FreeBSD subpartitions use relative block addresses whereas OpenBSD and NetBSD use absolute block addresses.

Here is a patch to Linux to adjust the FreeBSD partitions:

--- a/block/partitions/msdos.c  2015-12-27 18:17:37.000000000 -0800
+++ b/block/partitions/msdos.c  2015-12-29 10:44:25.813773357 -0800
@@ -300,6 +300,8 @@ static void parse_bsd(struct parsed_part
                        continue;
                bsd_start = le32_to_cpu(p->p_offset);
                bsd_size = le32_to_cpu(p->p_size);
+               if (memcmp(flavour, "bsd\0", 4) == 0)
+                       bsd_start = bsd_start + offset;
                if (offset == bsd_start && size == bsd_size)
                        /* full parent partition, we have it already */
                        continue;

Update 2017-05-29: This is now fixed in Linux-4.12-rc3 thanks to Christoph Hellwig and Jens Axboe and of course Linus.

[comet--berkeley]

This should be now fixed in Linux 4.4.73, 4.9.33, 4.11.6 and 4.12

[comet--berkeley]

There is a problem mounting older FreeBSD file systems using the original patch.

Here is a newer patch:

--- a/block/partitions/msdos.c.orig	2017-11-05 13:05:14.000000000 -0800
+++ b/block/partitions/msdos.c	2017-11-06 09:46:00.148228242 -0800
@@ -301,7 +301,9 @@ static void parse_bsd(struct parsed_part
  			continue;
  		bsd_start = le32_to_cpu(p->p_offset);
  		bsd_size = le32_to_cpu(p->p_size);
-		if (memcmp(flavour, "bsd\0", 4) == 0)
+		/* FreeBSD has relative offset if C partition offset is zero */
+		if (memcmp(flavour, "bsd\0", 4) == 0 &&
+		    le32_to_cpu(l->d_partitions[2].p_offset) == 0)
  			bsd_start += offset;
  		if (offset == bsd_start && size == bsd_size)
  			/* full parent partition, we have it already */