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From: Bodo Eggert <7eggert@gmx.de>
Subject: Re: [PATCH] vfs: added better file aio_read aio_write operations presence check
To: Manish Katiyar <mkatiyar@gmail.com>,
       Marco Stornelli <marco.stornelli@coritel.it>, viro@zeniv.linux.org.uk,
       linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
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Date: Tue, 16 Sep 2008 17:36:09 +0200
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Manish Katiyar <mkatiyar@gmail.com> wrote:
> On Tue, Sep 16, 2008 at 2:59 PM, Marco Stornelli
>> From: Marco Stornelli <marco.stornelli@gmail.com>

>> If a filesystem in the file operations specifies for read and write
>> operations only do_sync_read and do_sync_write without init aio_read and
>> aio_write, there will be a kernel oops, because the vfs code check the
>> presence of (to read for example) read OR aio_read method, then it calls read
>> if it's pointer is not null. It's not sufficient because if the read function
>> is actually a do_sync_read, it calls aio_read but without checking the
>> presence. I think a BUG_ON check can be more useful.
> 
> Instead of doing a BUG_ON() why can't we simply fall back to the
> generic_aio functions since most of the fs tend to do so as below.

> --- a/fs/read_write.c

> -             ret = filp->f_op->aio_read(&kiocb, &iov, 1, kiocb.ki_pos);
> +             if (filp->f_op->aio_read)
> +                     ret = filp->f_op->aio_read(&kiocb, &iov, 1, kiocb.ki_pos);
> +             else
> +                     ret = generic_file_aio_read(&kiocb, &iov, 1, kiocb.ki_pos);

Why can't the file system registration code set filp->f_op->aio_read to
generic_file_aio_read?