Re: [PATCH v2] CIFS: Print message when attempting a mount

[Steve French]

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@xxxxxxxxx>
> > To: rfreire@xxxxxxxxxx
> > Cc: "LKML" <linux-kernel@xxxxxxxxxxxxxxx>, "Steve French"
> > <sfrench@xxxxxxxxx>, "CIFS" <linux-cifs@xxxxxxxxxxxxxxx>, "Pavel Shilovsky"
> > <piastryyy@xxxxxxxxx>
> > 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@xxxxxxxxxx> 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@xxxxxxxxx>
> > > > To: rfreire@xxxxxxxxxx
> > > > Cc: "LKML" <linux-kernel@xxxxxxxxxxxxxxx>, "Steve French"
> > > > <sfrench@xxxxxxxxx>, "CIFS" <linux-cifs@xxxxxxxxxxxxxxx>, "Pavel
> > > > Shilovsky"
> > > > <piastryyy@xxxxxxxxx>
> > > > 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@xxxxxxxxxx> wrote:
> > > > > Hi Steve,
> > > > >
> > > > > ----- Original Message -----
> > > > > > From: "Steve French" <smfrench@xxxxxxxxx>
> > > > > > To: rfreire@xxxxxxxxxx
> > > > > > Cc: "LKML" <linux-kernel@xxxxxxxxxxxxxxx>, "Steve French"
> > > > > > <sfrench@xxxxxxxxx>, "CIFS" <linux-cifs@xxxxxxxxxxxxxxx>, "Pavel
> > > > > > Shilovsky"
> > > > > > <piastryyy@xxxxxxxxx>
> > > > > > 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@xxxxxxxxxx>
> > > > > > 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