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Message-ID: <3AE2680F.BED4CCFF@hacklab.net>
Date: Sat, 21 Apr 2001 22:11:43 -0700
From: PhiloVivero <pvspam-dntrepl@hacklab.net>
Reply-To: phiviv@hacklab.net
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To: linux-kernel@vger.kernel.org
CC: sebastien.godard@wanadoo.fr, timb@claire.org, axboe@suse.de,
        phiviv@hacklab.net
Subject: Device Major max and Disk Max in 2.4.x kernel
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I have a problem. Trying to write an iostat for Linux (or use an existing
one):

>From the kernel source:

[/usr/src/linux-2.4.2/include/linux] :) grep DK_MAX *.h
kernel_stat.h:#define DK_MAX_MAJOR 16
kernel_stat.h:#define DK_MAX_DISK 16

What to notice: MAJOR and DISK max are 16.

Again, from the kernel source:

[/usr/src/linux-2.4.2/fs/proc] :) grep -15 DK_MAX proc_misc.c
<snip>
    for (major = 0; major < DK_MAX_MAJOR; major++) {
            for (disk = 0; disk < DK_MAX_DISK; disk++) {
                    int active = kstat.dk_drive[major][disk] +
                            kstat.dk_drive_rblk[major][disk] +
                            kstat.dk_drive_wblk[major][disk];
                    if (active)
                            len += sprintf(page + len,
                                    "(%u,%u):(%u,%u,%u,%u,%u) ",
                                    major, disk,
                                    kstat.dk_drive[major][disk],
                                    kstat.dk_drive_rio[major][disk],
                                    kstat.dk_drive_rblk[major][disk],
                                    kstat.dk_drive_wio[major][disk],
                                    kstat.dk_drive_wblk[major][disk]
                    );
            }
    }

What to notice: We are looping up to the DK_MAX_MAJOR and DK_MAX_DISK. What
this means is, any major >16 or disk >16 won't be listed in /proc/stat under
the "disk_io" section.

Problem. On my system, which I figure is not too uncommon, I have several
partitions on two hard drives and a CDROM. They are configured thusly:

# cat /proc/partitions
major minor  #blocks  name
   3     0   20094480 hda
   3     1    6313513 hda1
   3     2     401625 hda2
   3     3   13374112 hda3
   3    64    4497152 hdb
  56     0   45034920 hdi
  56     1   22490968 hdi1
  56     2   22539195 hdi2

What to notice: I have a drive on /dev/hdi (never mind why, it actually works)
that is block major 56. Not only that, my cdrom device on /dev/hdb is block
major 3, but minor number 64. I am assuming for disks, minor == disk. Sorry if
this is an incorrect assumption.

No stats for /dev/hdi nor /dev/hdb ever show up in /proc/stat. Only for
/dev/hda. On my other 2.4.2 system, with multiple hard drives under 16/16,
I get multiple devices under /proc/stat.

The patch seems relatively easy. Change linux/include/linux/kernel_stat.h to
allow block major up to 56 (in my case... 64 in general???) and disks up to 64
(in my case).

But we might need more than 64 disks on a block major (there are MANY snips in
this so-called cut 'n' paste, because I figure you don't want to see them
all):

# l /dev/hd* | sort -n
brw-rw----    1 root     disk       3,  79 Feb 22 08:57 /dev/hdb15
brw-rw----    1 root     disk       3,  80 Feb 22 08:57 /dev/hdb16
brw-rw----    1 root     disk      22,  79 Feb 22 08:57 /dev/hdd15
brw-rw----    1 root     disk      22,  80 Feb 22 08:57 /dev/hdd16
brw-rw----    1 root     disk      33,  79 Feb 22 08:57 /dev/hdf15
brw-rw----    1 root     disk      33,  80 Feb 22 08:57 /dev/hdf16
brw-rw----    1 root     disk      34,  79 Feb 22 08:57 /dev/hdh15
brw-rw----    1 root     disk      34,  80 Feb 22 08:57 /dev/hdh16
brw-rw----    1 root     disk      56, 126 Mar 25 17:14 /dev/hdj62
brw-rw----    1 root     disk      56, 127 Mar 25 17:14 /dev/hdj63

What to notice: We have disks up to 127. I never see any block major over 64
on my system. The /dev/hdj device isn't used on my system. /dev/hdi and
/dev/hdj belong to a Promise RAID controller on a new-ish
ASUS AMD motherboard.

Let me know if I can be of further service. I must bashfully admit that I'm
not enough of a guru to recompile my kernel anymore, or I'd tweak the
kernel_stat.h file and recompile myself to test this.

This is just hazy recollection, but I think the 2.2.x kernels have the same
problem.

--
PhiloVivero
ps -- I'm not subscribed to this list, so if you want me to see replies...
please send to email!


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