/proc/partitions broken in 2.5.23

I got a bug report about an issue with LVM in 2.5.22-dj1, which turns out to be caused by broken /proc/partitions in mainline.

(davej@mesh:davej)$ cat /proc/partitions 
major minor  #blocks  name

8 0 0 sda
22 0 1515870810 hdc
22 64 1515870810 hdd

   3     0   29316672 hda
   3     1     117400 hda1
   3     2          1 hda2
   3     5     999904 hda5
   3     6    1499872 hda6
   3     7     683392 hda7
   3     8   26015944 hda8

3 64 1515870810 hdb

Note the huge numbers in hex are 0x5a5a5a5a, so something seems to be getting poisoned somewhere.

Also, should partitions with 0 blocks be showing up ? I don't recall that happening with the old-style 2.4 code.

Dave

| Dave Jones.        http://www.codemonkey.org.uk
| SuSE Labs

I changed something here a few weeks ago. The idea was to avoid listing partitions of size 0 but do list full devices, regardless of size. Especially in case of removable media that is useful. For example, a

	blockdev --rereadpt /dev/sda

might show that there is something there now.

Will look at what might cause your strange numbers. Unfortunately recent 2.5 kernels do not boot for me.

Andries

Seems it doesn't handle the case of 'no media in drive' too well. hdc - cdrom, hdd - zip drive, hdb - no device there.

hda2 is odd looking too showing a #blocks of '1', when it's actually..

Device Boot Start End Blocks Id System
/dev/hda2 234 58168 29199240 5 Extended

Oddly, on another machine, it detects an LS-120 drive with no media correctly..
22 64 0 hdd

(but still gets the 'no device' case wrong on that box).

Dave.

| Dave Jones.        http://www.codemonkey.org.uk
| SuSE Labs

That is correct, and something I did before you were born.

An extended partition is a box containing logical partitions. It is almost always an error when people want to write directly to it (confusing the extended partition with some logical partition inside). After a number of reports of people who messed up their disk by doing mkswap or mkfs on an extended partition I changed the length of an extended partition to 1 block, enough for LILO but stopping mkswap and mkfs.
People who really want to access these blocks, like e.g. fdisk, can do so via /dev/hda.

Andries

Ah, that makes perfect sense to me now.

Dave.

| Dave Jones.        http://www.codemonkey.org.uk
| SuSE Labs

I traced the change to the part of mainline ChangeSet 1.496 given below (warning: cut and pasted). It seems to cause every possible device that a driver could provide to show up in /proc/partitions. For LVM, that's a zillion devices, and /proc/partitions overflows, showing some random pages from memory. Reverting the patch below makes /proc/partitions and LVM happy again.

Cheers,
Wayne

@@ -177,9 +177,10 @@
 	if (sgp == gendisk_head)
 		seq_puts(part, "major minor  #blocks  name\n\n");
 
-	/* show all non-0 size partitions of this disk */
+	/* show the full disk and all non-0 size partitions of it */
 	for (n = 0; n < (sgp->nr_real << sgp->minor_shift); n++) {
-		if (sgp->part[n].nr_sects == 0)
+		int minormask = (1<<sgp->minor_shift) - 1;
+		if ((n & minormask) && sgp->part[n].nr_sects == 0)
 			continue;
 		seq_printf(part, "%4d  %4d %10d %s\n",
 			sgp->major, n, sgp->sizes[n],