[Crash-utility] Crash-utility Digest, Vol 86, Issue 13
俞永明
yuym.fnst at cn.fujitsu.com
Mon Nov 12 09:17:00 UTC 2012
Hello, Dave,
To begin with, I am sincerely grateful for your detailed suggestions.
I have read the suggetions you gave and finished modifying the relative
parts. The following will demonstrate the modifications.
The first is when it comes to older kernels that do not have cgroups, it
now offers justification of whether the kernel have cgroups and output
information when the kernel do not contain cgroup.
Secondly, you mentioned the cgroups "unabled" in the previous mail,
considerring those inactive cgroups whose root(cgroupfs_root) is not
linked by the active root list, I prefer to display something when there
are no active cgroups other than output the inactive cgroups.
If the inactive cgroups' information is needy, I need to rethink and
find another way to get target data structure.
Thirdly, the unnecessary -h option was deleted and help information was
corrected according to your suggestions.
Lastly, the changed "lscgroup" command add the address of cgroup when
displaying cgroups. For the reason that address length is fixed on a
certain system, the first column of output is used to display the address.
You can check the modifications in the attachment by the same operation
as said in last mail.
Lots of thanks.
Yongming Yu
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> 1. Re: [Crash] [PATCH] add a new command: lscgroup (Dave Anderson)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 9 Nov 2012 14:52:51 -0500 (EST)
> From: Dave Anderson <anderson at redhat.com>
> To: "Discussion list for crash utility usage, maintenance and
> development" <crash-utility at redhat.com>
> Subject: Re: [Crash-utility] [Crash] [PATCH] add a new command:
> lscgroup
> Message-ID:
> <1824583457.29845585.1352490771952.JavaMail.root at redhat.com>
> Content-Type: text/plain; charset=utf-8
>
>
>
> ----- Original Message -----
>> Hello Dave,
>>
>> I have been working on a new command named lscgroup to
>> list cgroups' information and finished it recently.
>>
>> This command displays all the cgroups' information or the
>> appointed cgroups' information relatively according to user's
>> input. The following shows the two types of output.
>>
>> 1.Display all the cgroups' information of the system.
>> crash> lscgroup
>> blkio:/
>> blkio:/libvirt
>> blkio:/libvirt/lxc
>> blkio:/libvirt/qemu
>> net_cls:/
>> ...
>> ...
>> cpuset:/
>> cpuset:/libvirt
>> cpuset:/libvirt/lxc
>> cpuset:/libvirt/qemu
>>
>>
>> 2.Display the appointed cgroups' information.
>> crash> lscgroup memory:/ cpuset:/libvirt
>> memory:/
>> memory:/libvirt
>> memory:/libvirt/lxc
>> memory:/libvirt/qemu
>> cpuset:/libvirt
>> cpuset:/libvirt/lxc
>> cpuset:/libvirt/qemu
>>
>> To see more details, please refer to the help information and the patch.
>>
>> To build the module from the top-level crash-<version> directory,
>> enter:
>> $ cp <path-to>/lscgroup.c extensions
>> $ make extensions
>
> Thanks for diving into this kernel subsystem. Given the emergence
> of cgroups, this command could ultimately be considered as a new
> built-in command.
>
> However, that being said, it does need some additional work.
>
> First, for older kernels that don't have cgroups, there should be a
> protection mechanism to prevent this from happening:
>
> crash> sys | grep RELEASE
> RELEASE: 2.6.18-146.el5
> crash> lscgroup
>
> lscgroup: invalid structure member offset: cgroupfs_root_root_list
> FILE: lscgroup.c LINE: 503 FUNCTION: cgroup_list_cgroups()
>
> [/usr/bin/crash] error trace: 4611e1 => 7f3b8f3a19d7 => 7f3b8f3a14e6 => 50b701
>
> 50b701: OFFSET_verify+161
> 4611e1: exec_command+801
>
> lscgroup: invalid structure member offset: cgroupfs_root_root_list
> FILE: lscgroup.c LINE: 503 FUNCTION: cgroup_list_cgroups()
>
> crash>
>
> You should check for the existence of a kernel variable or structure definition,
> and if they don't exist, call command_not_supported().
>
> Secondly, if I am not mistaken, your command only shows "enabled" cgroups?
> So for example, on this RHEL6 system, the command quietly does nothing:
>
> crash> sys | grep RELEASE
> RELEASE: 2.6.32-15.el6.x86_64
> crash> lscgroup
> crash>
>
> Is that the case? I wonder if you should also show cgroups that are
> not enabled, i.e., like /proc/cgroups does? Or at a minimum, it should
> show display something like "(no cgroups enabled)" instead of just
> showing nothing at all.
>
> Thirdly, your help page shows a "-h" option, which is unnecessary:
>
> crash> help lscgroup
>
> NAME
> lscgroup - list all cgroups
>
> SYNOPSIS
> lscgroup lscgroup [<controllers>:<path>] [...][-h]
>
> ...
>
> because it doesn't do anything other than show the SYNOPSIS line
> from the "help lscgroup" output:
>
> crash> lscgroup -h
> Usage:
> lscgroup lscgroup [<controllers>:<path>] [...][-h]
> Enter "help lscgroup" for details.
> crash>
>
> And you should change the third line in help_lscgroup[] from:
>
> char *help_lscgroup[] = {
> "lscgroup",
> "list all cgroups",
> "lscgroup [<controllers>:<path>] [...][-h]",
>
> to:
>
> "[<controllers>:<path>] [...][-h]",
>
> so that "lscgroup" is not printed twice in the "help lscgroup" and
> the "Usage:" output.
>
>
> And lastly, and most importantly, is what the command
> does *not* show.
>
> Consider that most crash commands that delve into kernel
> subsystems typically show information intermingled with
> key data structure addresses. So if there is a bug associated
> with a kernel subsystem, the data structure addresses displayed
> by a crash command can be used as a starting point for debugging
> purposes.
>
> So for example, if there was a bug associated with cgroups, your
> command's output only shows the name strings, but there's nothing
> else to "work with" for debugging. Wouldn't it be more helpful to
> at least display the cgroup and/or the cgroupfs_root addresses?
> Then there would be useful data structure addresses to start with.
>
> Thanks,
> Dave
>
>
>
>
>
>
>
>
>
>
>
>
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> End of Crash-utility Digest, Vol 86, Issue 13
> *********************************************
>
>
--
--------------------------------------------------
Yu Yongming
Nanjing Fujitsu Nanda Software Tech. Co., Ltd.
(FNST)No. 6 Wenzhu Road, Nanjing, 210012, China
EMail：yuym.fnst at cn.fujitsu.com
Regards__
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