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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 14 Aug 2018 09:22:10 -0700
Message-ID: <CA+55aFwyCmYfUrGt61d-6B=1XiTLoudNO=_bQ9-g_rDg8Ao_VA@mail.gmail.com>
Subject: Re: Warning when using eMMC and partprobe: generic_make_request:
 Trying to write to read-only block-device
To:     Ilya Dryomov <idryomov@gmail.com>
Cc:     stefan@agner.ch, Jens Axboe <axboe@kernel.dk>,
        Sagi Grimberg <sagi@grimberg.me>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Tue, Aug 14, 2018 at 8:24 AM Ilya Dryomov <idryomov@gmail.com> wrote:
>
> Looks like it's coming from that fsync():
>
>   sys_fsync
>     do_fsync
>       vfs_fsync_range
>         blkdev_fsync
>           blkdev_issue_flush
>
> I think we need to teach blkdev_issue_flush() to bail out if the bdev
> is read-only, similar to blkdev_issue_discard(), _write_zeroes(), etc.
> The question is which error code to use.  blkdev_fsync() already skips
> over EOPNOTSUPP, so it is a (no-so-good) option.  Other blkdev_issue_
> functions return EPERM.

Oh, just make issue_flush() return EROFS for a read-only device.

Or maybe we should even just consider the flush to be a read operation?

But I guess the error code gets percolated all the way to user space?
The safest option might just be to return 0.

               Linus