Re: [EXPERIMENT v2] new mount API verbose errors from userspace

[Steve French <smfrench@gmail.com>]

Tentatively merged into cifs-2.6.git for-next but would like more
feedback on other's thoughts on this. Getting more verbose error
information back on mount errors (to userspace returning something
more than a primitive small set of return codes, and a message logged
to dmesg) is critical, and this approach seems reasonable at first
glance but if there are better ways ...

On Thu, Mar 18, 2021 at 8:12 AM Aurélien Aptel <aaptel@suse.com> wrote:
>
>
> Since there's no standard VFS way to get the supported mount options
> from userspace, I thought I would do what Ronnie suggested and export
> them from a cifs /proc file.
> That's the only change since v1, in the 4th patch.
>
> David, maybe this can give your arguments for the need for fsinfo() if
> we end up using this in cifs-utils.
>
> I have added some dumb code in userspace to parse it and see if the
> option exists and what type it is. This removes the requirement of
> having to keep cifs-utils and kernel updated at the same time to use new
> options.
>
> Previous intro
> =======================================================================
> I have some code to use the new mount API from user space.
>
> The kernel changes are just making the code use the fs_context logging
> feature.
>
> The sample userspace prog (fsopen.c attached) is just a PoC showing how
> mounting is done and how the mount errors are read.
>
> If you change the prog to use a wrong version for example (vers=4.0) you
> get this:
>
>     $ gcc -o fsopen fsopen.c
>     $ ./fsopen
>     fsconfig(sfd, FSCONFIG_SET_STRING, "vers", "4.0", 0): Invalid argument
>     kernel mount errors:
>     e Unknown vers= option specified: 4.0
>
> The pros are that we process one option at a time and we can fail early
> with verbose, helpful messages to the user.
> =======================================================================
>
>
>
> Cheers,
> --
> Aurélien Aptel / SUSE Labs Samba Team
> GPG: 1839 CB5F 9F5B FB9B AA97  8C99 03C8 A49B 521B D5D3
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-- 
Thanks,

Steve