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Subject: Re: [PATCH v2] CIFS: Print message when attempting a mount
To:     Rodrigo Freire <rfreire@redhat.com>,
        Steve French <smfrench@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        CIFS <linux-cifs@vger.kernel.org>,
        Pavel Shilovsky <piastryyy@gmail.com>,
        linux-fsdevel@vger.kernel.org
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From:   Steve French <sfrench@samba.org>
Message-ID: <a24927eb-2c52-4b19-f9ae-c88b2c129c60@samba.org>
Date:   Sat, 6 Oct 2018 12:13:20 -0500
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Comparing what other file systems print to dmesg at mount time is 
interesting - just tried it for  four file systems, two log nothing by 
default, two log something. See below.


BTRFS:

root@smf-Thinkpad-P51:~/# mount /btrfs
root@smf-Thinkpad-P51:~/c# dmesg
[96283.701117] BTRFS info (device mmcblk0p1): disk space caching is enabled
[96283.701121] BTRFS info (device mmcblk0p1): has skinny extents
[96283.708477] BTRFS info (device mmcblk0p1): enabling ssd optimizations


EXT4:

root@smf-Thinkpad-P51:~# mount /dev/nvme0n1p6 /ext4
root@smf-Thinkpad-P51:~# dmesg
[96654.422038] EXT4-fs (nvme0n1p6): mounted filesystem with ordered data 
mode. Opts: (null)


VFAT:

root@smf-Thinkpad-P51:~# mount /dev/nvme0n1p1 /fat
root@smf-Thinkpad-P51:~# dmesg
root@smf-Thinkpad-P51:~#


NFS (it logs messages first time the module is loaded, for the 
id_resolver, but not for the mount):

root@smf-Thinkpad-P51:~# mount -t nfs localhost:/nfsexport /nfs
root@smf-Thinkpad-P51:~# dmesg
root@smf-Thinkpad-P51:~#


On 10/02/2018 04:53 PM, Rodrigo Freire wrote:
> Hi hi again Steve \o
>
> I do see potential for a ftrace rewrite for the cifs_dbg messages.
>
> But for the original post, I am aiming for a message to be printed
> and found in dmesg, helping to correlate and troubleshoot events in
> production systems.
>
> So given the debugging nature of ftrace, this is not of help for my
> patch request.
>
> So, ACK for v2, using cifs_dbg(VFS) which actually translates to a
> pr_warn(), or request a V3 using pr_info() (which I am absolutely fine
> with) or...?
>
> Let me know.
>
> I appreciate your time and review!
>
> - RF.
>
> ----- Original Message -----
>
>> From: "Steve French" <smfrench@gmail.com>
>> To: rfreire@redhat.com
>> Cc: "LKML" <linux-kernel@vger.kernel.org>, "Steve French"
>> <sfrench@samba.org>, "CIFS" <linux-cifs@vger.kernel.org>, "Pavel Shilovsky"
>> <piastryyy@gmail.com>
>> Sent: Tuesday, October 2, 2018 6:25:46 PM
>> Subject: Re: [PATCH v2] CIFS: Print message when attempting a mount
>> It is an interesting question - my gut reaction is that messages that
>> need more immediate attention should be logged as KERN_ERR (similar to
>> cifs_dbg(VFS ...) but given how easy it is now to use dynamic tracing
>> and better to read, if a developer would need it ... probably best to
>> use ftrace (trace-cmd). Note that xfs has more than 570 (!) dynamic
>> trace point callouts now vs. fewer than 30 for xfs_notice
>> On Tue, Oct 2, 2018 at 4:20 PM Rodrigo Freire <rfreire@redhat.com> wrote:
>>> Hi Steve o/
>>>
>>> I personally like more a pr_info() instead of a cifs_dbg (which wraps to a
>>> pr_warn). But in order to keep in line with the general CIFS coding style
>>> I stuck to cifs_dbg
>>>
>>> But I would happily rewrite the cifs_dbg to pr_info a v3: That would be
>>> good enough too.
>>>
>>> Ah for what is worth my test/target systems are CentOS/Red Hat Enterprise
>>> Linux.
>>>
>>> Thoughts?
>>>
>>> Thanks!
>>>
>>> - RF.
>>>
>>> ----- Original Message -----
>>>> From: "Steve French" <smfrench@gmail.com>
>>>> To: rfreire@redhat.com
>>>> Cc: "LKML" <linux-kernel@vger.kernel.org>, "Steve French"
>>>> <sfrench@samba.org>, "CIFS" <linux-cifs@vger.kernel.org>, "Pavel
>>>> Shilovsky"
>>>> <piastryyy@gmail.com>
>>>> Sent: Tuesday, October 2, 2018 5:35:49 PM
>>>> Subject: Re: [PATCH v2] CIFS: Print message when attempting a mount
>>>> I noticed that on at least the first system I looked at (Ubuntu 18.04)
>>>> it defaults to KERN_WARNING (ie 4) so wouldn't have shown a KERN_INFO
>>>> which is level 6 (as the mount example from ext4) by default
>>>> or the xfs_notice (which is level 5)
>>>> https://elinux.org/Debugging_by_printing
>>>> On Tue, Oct 2, 2018 at 2:28 PM Rodrigo Freire <rfreire@redhat.com> wrote:
>>>>> Hi Steve,
>>>>>
>>>>> ----- Original Message -----
>>>>>> From: "Steve French" <smfrench@gmail.com>
>>>>>> To: rfreire@redhat.com
>>>>>> Cc: "LKML" <linux-kernel@vger.kernel.org>, "Steve French"
>>>>>> <sfrench@samba.org>, "CIFS" <linux-cifs@vger.kernel.org>, "Pavel
>>>>>> Shilovsky"
>>>>>> <piastryyy@gmail.com>
>>>>>> Sent: Tuesday, October 2, 2018 4:17:02 PM
>>>>>> Subject: Re: [PATCH v2] CIFS: Print message when attempting a mount
>>>>>>
>>>>>> Are you sure that these aren't logged by the automounter (for ext4,
>>>>>> xfs etc.). When I looked in my dmesg logs I didn't find matching log
>>>>>> entries in the file systems themselves. Do you have an example?
>>>>> I'm positive about it. Check it out:
>>>>>
>>>>> [rfreire@rf ~]$ cd git/upstream/fs/ext4/
>>>>> [rfreire@rf ext4]$
>>>>> [rfreire@rf ext4]$
>>>>> [rfreire@rf ext4]$ grep -r "mounted filesystem with"
>>>>> super.c: ext4_msg(sb, KERN_INFO, "mounted filesystem with%s. "
>>>>>
>>>>>
>>>>> [rfreire@rf ext4]$ dmesg | grep mount
>>>>> [ 21.550897] EXT4-fs (dm-1): mounted filesystem with ordered data mode.
>>>>> Opts: (null)
>>>>> [ 22.216213] EXT4-fs (dm-1): re-mounted. Opts: discard
>>>>> [ 22.598267] EXT4-fs (sda1): mounted filesystem with ordered data mode.
>>>>> Opts: (null)
>>>>> [ 22.605225] EXT4-fs (sdc): mounted filesystem without journal. Opts:
>>>>> discard
>>>>> [ 24.029161] EXT4-fs (dm-2): mounted filesystem with ordered data mode.
>>>>> Opts: (null)
>>>>> [ 24.047777] EXT4-fs (dm-4): mounted filesystem without journal. Opts:
>>>>> (null)
>>>>>
>>>>> XFS sample dmesg (from
>>>>> https://www.reddit.com/r/archlinux/comments/40b9r9/xfs_partition_is_mounted_during_boot_and_then/):
>>>>>
>>>>> [ 2.764491] XFS (sdb1): Mounting V5 Filesystem
>>>>> [ 3.200886] XFS (sdb1): Ending clean mount
>>>>> [ 5.384218] XFS (sdb1): Unmounting Filesystem
>>>>>
>>>>> Relevant code:
>>>>>
>>>>> [rfreire@rf ~]$ cd ../xfs
>>>>>
>>>>> [rfreire@rf xfs]$ grep "Mounting V" *.c
>>>>> xfs_log.c: xfs_notice(mp, "Mounting V%d Filesystem",
>>>>>
>>>>>
>>>>>> On the idea of adding cifsFYI logging here - I slightly prefer using
>>>>>> ftrace (trace-cmd, ie dynamic tracing) so there is less overhead and
>>>>>> easier to turn on/off following the example of xfs, f2fs, nfs, nfsd
>>>>>> etc.
>>>>> Remember that cifsFYI already exists; I just moved it inside a if
>>>>> clause
>>>>> to print it only when running under debug. (they way it is originally).
>>>>>
>>>>>> On Tue, Oct 2, 2018 at 6:57 AM Rodrigo Freire <rfreire@redhat.com>
>>>>>> wrote:
>>>>>>> Currently, no messages are printed when mounting a CIFS filesystem
>>>>>>> and
>>>>>>> no debug configuration is enabled.
>>>>>>>
>>>>>>> However, a CIFS mount information is valuable when troubleshooting
>>>>>>> and/or forensic analyzing a system and finding out if was a CIFS
>>>>>>> endpoint mount attempted.
>>>>>>>
>>>>>>> Other filesystems such as XFS, EXT* does issue a printk() when
>>>>>>> mounting
>>>>>>> their filesystems.
>>>>>
>>>>>> --
>>>>>> Thanks,
>>>>> Thank You! o/
>>>> --
>>>> Thanks,
>>>> Steve
>> --
>> Thanks,
>> Steve