/proc/partitions broken in 2.5.23

/proc/partitions broken in 2.5.23

[Dave Jones]

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

Re: /proc/partitions broken in 2.5.23

[Andries Brouwer]

On Wed, Jun 19, 2002 at 10:02:48AM +0100, Dave Jones wrote:

> 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.

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

Re: /proc/partitions broken in 2.5.23

[Dave Jones]

On Wed, Jun 19, 2002 at 01:32:33PM +0200, Andries Brouwer wrote:

 > >   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
 > 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.

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

Re: /proc/partitions broken in 2.5.23

[Andries Brouwer]

On Wed, Jun 19, 2002 at 01:44:02PM +0200, Dave Jones wrote:

> 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 

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

Re: /proc/partitions broken in 2.5.23

[Dave Jones]

On Wed, Jun 19, 2002 at 02:51:54PM +0200, Andries Brouwer wrote:

 > 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.

Ah, that makes perfect sense to me now.

        Dave.


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

Re: /proc/partitions broken in 2.5.23

[Wayne Whitney]

In mailing-lists.linux-kernel, you wrote:

> 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.

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


--- a/drivers/block/genhd.c	Wed May  8 09:53:06 2002
+++ b/drivers/block/genhd.c	Sun Jun  9 18:58:36 2002
@@ -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],

Re: /proc/partitions broken in 2.5.23

[Andries.Brouwer]

On Wed, Jun 19, 2002 at 10:02:48AM +0100, Dave Jones wrote:

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

Is this LVM?

I don't see how LVM could produce such values.
(And in fact LVM does not even compile, so only a patched LVM
could produce anything at all.)



From: Wayne Whitney <whitney@adsl-209-76-109-63.dsl.snfc21.pacbell.net>

    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.


    --- a/drivers/block/genhd.c    Wed May  8 09:53:06 2002
    +++ b/drivers/block/genhd.c    Sun Jun  9 18:58:36 2002
    @@ -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],

Yes.
Normally the nr_real field indicates how many devices are
present. But LVM sets that to 256 even when nothing is present.
So, indeed, when all size fields are set to 0 this would probably
yield a list of 256 absent LVM devices.
Maybe LVM has to be fixed, or this patch fragment reverted, or both.

Something else is that if /proc/partitions overflows that must be
fixed independently of zeros or LVM.

Andries

Re: /proc/partitions broken in 2.5.23

[Dave Jones]

On Fri, Jun 21, 2002 at 01:21:40AM +0200, Andries.Brouwer@cwi.nl wrote:

 >     > 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
 >     > 
 >     > Note the huge numbers in hex are 0x5a5a5a5a, so something
 >     > seems to be getting poisoned somewhere.
 > 
 > Is this LVM?

No.
 
 > I don't see how LVM could produce such values.
 > (And in fact LVM does not even compile, so only a patched LVM
 > could produce anything at all.)

The original person who reported a problem to me used LVM, and 
in the course of discussion, the proc/partitions bug came to light.
The values pasted above are from a box with no LVM compiled.

 > Normally the nr_real field indicates how many devices are
 > present. But LVM sets that to 256 even when nothing is present.
 > So, indeed, when all size fields are set to 0 this would probably
 > yield a list of 256 absent LVM devices.
 > Maybe LVM has to be fixed, or this patch fragment reverted, or both.

As I mentioned in another mail, it seems that removable devices with
no media have no valid #blocks, and is thus getting poisoned.

        Dave

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

Re: /proc/partitions broken in 2.5.23

[Anders Gustafsson]

On Fri, Jun 21, 2002 at 01:21:40AM +0200, Andries.Brouwer@cwi.nl wrote:
>     > 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
>     > 
>     > Note the huge numbers in hex are 0x5a5a5a5a, so something
>     > seems to be getting poisoned somewhere.
> 
> Is this LVM?
> 
> I don't see how LVM could produce such values.
> (And in fact LVM does not even compile, so only a patched LVM
> could produce anything at all.)

Me neither. And as a datapoint: with my lvm-cleanup-patch I get
correct size-values for all my partitions (but, yes, all 0-sized LVs
shows). But there is a problem with my /proc/partitions, i starts with
2 pages of garbage (8k). Is this some kind of overflow problem as lvm
creates 256 entries? 


-- 

//anders/g

Re: /proc/partitions broken in 2.5.23

[Peter Chubb]

Here's a fix that works for me (the /proc/partitions output is still broken in
2.5.24 -- it appears to be following sgp->part[n] pointers that aren't
initialised)

--- /tmp/geta29820	Wed Jun 26 13:16:14 2002
+++ linux-2.5.24/drivers/block/genhd.c	Wed Jun 26 11:50:36 2002
@@ -179,8 +179,7 @@
 
 	/* show the full disk and all non-0 size partitions of it */
 	for (n = 0; n < (sgp->nr_real << sgp->minor_shift); n++) {
-		int minormask = (1<<sgp->minor_shift) - 1;
-		if ((n & minormask) && sgp->part[n].nr_sects == 0)
+		if (sgp->sizes[n] == 0)
 			continue;
 		seq_printf(part, "%4d  %4d %10llu %s\n",
 			sgp->major, n, (unsigned long long)sgp->sizes[n],
--- /tmp/geta29832	Wed Jun 26 13:17:36 2002
+++ linux-2.5.24/drivers/ide/probe.c	Wed Jun 26 11:10:00 2002
@@ -1146,6 +1146,7 @@
 	gd->sizes = kmalloc(ATA_MINORS * sizeof(gd->sizes[0]), GFP_KERNEL);
 	if (!gd->sizes)
 		goto err_kmalloc_gd_sizes;
+	memset(gd->sizes, 0, ATA_MINORS*sizeof(gd->sizes[0]));
 
 	gd->part = kmalloc(ATA_MINORS * sizeof(struct hd_struct), GFP_KERNEL);
 	if (!gd->part)