linux-kernel - Re: [PATCH] vfs: added better file aio_read aio

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Date:	Tue, 16 Sep 2008 13:13:34 +0200
From:	Marco Stornelli <marco.stornelli@...itel.it>
To:	Manish Katiyar <mkatiyar@...il.com>
Cc:	viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfs: added better file aio_read aio_write operations
 presence check

BUG_ON it was a way to say: "hey you've used the do_sync_read/write as
read/write operation but you don't specified an aio_read/write", but
your solutions it's good too.

Manish Katiyar ha scritto:
> On Tue, Sep 16, 2008 at 2:59 PM, Marco Stornelli
> <marco.stornelli@...itel.it> wrote:
>> From: Marco Stornelli <marco.stornelli@...il.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.
> 
> 
> Signed-off-by: Manish Katiyar <mkatiyar@...il.com>
> 
> ---
>  fs/read_write.c |   10 ++++++++--
>  1 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 9ba495d..5439bc4 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -225,7 +225,11 @@ ssize_t do_sync_read(struct file *filp, char
> __user *buf, size_t len, loff_t *pp
>  	kiocb.ki_left = len;
> 
>  	for (;;) {
> -		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);
>  		if (ret != -EIOCBRETRY)
>  			break;
>  		wait_on_retry_sync_kiocb(&kiocb);
> @@ -280,7 +284,10 @@ ssize_t do_sync_write(struct file *filp, const
> char __user *buf, size_t len, lof
>  	kiocb.ki_left = len;
> 
>  	for (;;) {
> -		ret = filp->f_op->aio_write(&kiocb, &iov, 1, kiocb.ki_pos);
> +		if (filp->f_op->aio_write)
> +			ret = filp->f_op->aio_write(&kiocb, &iov, 1, kiocb.ki_pos);
> +		else
> +			ret = generic_file_aio_write(&kiocb, &iov, 1, kiocb.ki_pos);
>  		if (ret != -EIOCBRETRY)
>  			break;
>  		wait_on_retry_sync_kiocb(&kiocb);

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