linux-kernel - Re: Userspace regression with 6baca7601bde ("scsi: target: drop unused pi_prot

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Date:   Mon, 4 Feb 2019 01:40:48 +0100
From:   David Disseldorp <ddiss@...e.de>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Christoph Hellwig <hch@....de>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
        linux-scsi@...r.kernel.org, target-devel@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Lee Duncan <lduncan@...e.com>
Subject: Re: Userspace regression with 6baca7601bde ("scsi: target: drop
 unused pi_prot_format attribute storage")

Hi Laura,

Thanks for the report...

On Sun, 3 Feb 2019 17:56:00 +0100, Laura Abbott wrote:

> Fedora got a bug report of a new permission denied error with 5.0-rc2:
> 
> >   File "/usr/lib/python3.7/site-packages/rtslib_fb/utils.py", line 100, in fread
> >     with open(path, 'r') as file_fd:
> > PermissionError: [Errno 13] Permission denied: '/sys/kernel/config/target/core/fileio_28/xxx/attrib/pi_prot_format'  
> 
> This looks like an intentional behavior change with
> 
> commit 6baca7601bdee2e57f20c45d63eb53b89b33e816
> Author: David Disseldorp <ddiss@...e.de>
> Date:   Fri Nov 23 18:36:11 2018 +0100
> 
>      scsi: target: drop unused pi_prot_format attribute storage
>      
>      On write, the pi_prot_format configfs attribute invokes the device
>      format_prot() callback if present. Read dumps the contents of
>      se_dev_attrib.pi_prot_format which is always zero.  Make the configfs
>      attribute write-only, and drop the always zero se_dev_attrib.pi_prot_format
>      storage.
>      
>      Signed-off-by: David Disseldorp <ddiss@...e.de>
>      Reviewed-by: Christoph Hellwig <hch@....de>
>      Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
> 
> 
> Unfortunately, existing code that's opening with read permissions is now broken.
> Can this be reverted? Full bug at https://bugzilla.redhat.com/show_bug.cgi?id=1667505

Lee (cc'ed) pinged me a couple of days ago about the same issue.
My preference would be to add back a dummy read handler without the
corresponding (unused) se_dev_attrib.pi_prot_format member.
I'll prepare something tomorrow with this, but if it's urgent then I'd
also be okay with a straight revert.

Cheers, David