linux-kernel - Re: [PATCH v2 03/24] erofs: add super block operations

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Message-ID: <7774f181-a41c-f30a-3b2a-02d7438d3509@huawei.com>
Date:   Sun, 21 Jul 2019 12:12:15 +0800
From:   Gao Xiang <gaoxiang25@...wei.com>
To:     Al Viro <viro@...iv.linux.org.uk>
CC:     Gao Xiang <hsiangkao@....com>, <devel@...verdev.osuosl.org>,
        Theodore Ts'o <tytso@....edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Miao Xie <miaoxie@...wei.com>, <linux-erofs@...ts.ozlabs.org>,
        LKML <linux-kernel@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 03/24] erofs: add super block operations



On 2019/7/21 12:05, Al Viro wrote:
> On Sun, Jul 21, 2019 at 11:08:42AM +0800, Gao Xiang wrote:
> 
>> It is for debugging use as you said below, mainly for our internal
>> testers whose jobs are
>> to read kmsg logs and catch kernel problems. sb->s_id (device number)
>> maybe not
>> straight-forward for them compared with dev_name...
> 
> Huh? ->s_id is something like "sdb7" - it's bdev_name(), not a device
> number...

You are right. Forgive me, actually we use /dev/block/by-name/system
to mount fs... we have to do some lookup if using sdbX instead.


> 
>> The initial purpose of erofs_mount_private was to passing multi private
>> data from erofs_mount
>> to erofs_read_super, which was written before fs_contest was introduced.
> 
> That has nothing to do with fs_context (well, other than fs_context conversions
> affecting the code very close to that).

OK. That is fine.

> 
>> I agree with you, it seems better to just use s_id in community and
>> delete erofs_mount_private stuffs...
>> Yet I don't look into how to use new fs_context, could I keep using
>> legacy mount interface and fix them all?
> 
> Sure.
> 
>> I guess if I don't misunderstand, that is another suggestion -- in
>> short, leave all destructors to .kill_sb() and
>> cleanup fill_super().
> 
> Just be careful with that iput() there - AFAICS, if fs went live (i.e.
> if ->s_root is non-NULL), you really need it done only from put_super();
> OTOH, for the case of NULL ->s_root ->put_super() won't be called at all,
> so in that case you need it directly in ->kill_sb().

I got it. I will do a quick try now :) But in case of introducing issues,
I guess I need to do some fault injection by hand.....

Thanks,
Gao Xiang

>