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

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Date:	Tue, 16 Sep 2008 16:33:24 +0530
From:	"Manish Katiyar" <mkatiyar@...il.com>
To:	"Marco Stornelli" <marco.stornelli@...itel.it>
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

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);
-- 
1.5.4.3


Thanks -
Manish

> Signed-off-by: Marco Stornelli <marco.stornelli@...il.com>
> ---
>
> --- linux-2.6.26.5/fs/read_write.c.orig 2008-08-20 20:11:37.000000000 +0200
> +++ linux-2.6.26.5/fs/read_write.c      2008-09-16 11:01:13.000000000 +0200
> @@ -240,6 +240,7 @@ ssize_t do_sync_read(struct file *filp,
>        kiocb.ki_pos = *ppos;
>        kiocb.ki_left = len;
>
> +       BUG_ON(!filp->f_op->aio_read);
>        for (;;) {
>                ret = filp->f_op->aio_read(&kiocb, &iov, 1, kiocb.ki_pos);
>                if (ret != -EIOCBRETRY)
> @@ -295,6 +296,7 @@ ssize_t do_sync_write(struct file *filp,
>        kiocb.ki_pos = *ppos;
>        kiocb.ki_left = len;
>
> +       BUG_ON(!filp->f_op->aio_write);
>        for (;;) {
>                ret = filp->f_op->aio_write(&kiocb, &iov, 1, kiocb.ki_pos);
>                if (ret != -EIOCBRETRY)
>
> --
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