Hi,
On Tue, 2010-09-28 at 21:52 +0200, Geert Uytterhoeven wrote:
> On Tue, Sep 28, 2010 at 19:07, Janjaap Bos <janj...@bos.nl> wrote:
> > See attached patch, and earlier message posted in March 2010 on uml user
> > list. We are out of maintainer...
>
> Thanks for the patch!
>
> | --- a/arch/um/drivers/ubd_kern.c
> | +++ b/arch/um/drivers/ubd_kern.c
> | @@ -1223,7 +1227,7 @@ static void do_ubd_request(struct request_queue *q)
> | struct io_thread_req *io_req;
> | struct request *req;
> | sector_t sector;
> | - int n;
> | + int n, last_sectors;
> |
> | while(1){
> | struct ubd *dev = q->queuedata;
> | @@ -1239,9 +1243,12 @@ static void do_ubd_request(struct request_queue *q)
> |
> | req = dev->request;
> | sector = blk_rq_pos(req);
> | + last_sectors = 0;
> | while(dev->start_sg < dev->end_sg){
> | struct scatterlist *sg = &dev->sg[dev->start_sg];
> |
> | + sector += last_sectors;
> | + last_sectors = 0;
> | io_req = kmalloc(sizeof(struct io_thread_req),
> | GFP_ATOMIC);
> | if(io_req == NULL){
> | @@ -1253,7 +1260,7 @@ static void do_ubd_request(struct request_queue *q)
> | (unsigned long long)sector << 9,
> | sg->offset, sg->length, sg_page(sg));
> |
> | - sector += sg->length >> 9;
> | + last_sectors = sg->length >> 9;
> | n = os_write_file(thread_fd, &io_req,
> | sizeof(struct io_thread_req *));
> | if(n != sizeof(struct io_thread_req *)){
>
> However, I'm wondering what difference this part makes?
>
It fixes ubd block handling integrity.
With large block operations errors occurred. Probably due to lost
request pointers as explained below. Need to keep a local count of
sectors and delay the update. Done by reverting commit
f81f2f7c9fee307e371f37424577d46f9eaf8692 using the present
block api. (At least which is what I intend, but perhaps quite likely I
am missing the point, also it may not be needed anymore if only single
512 byte sector blocks are used per request. Anyway... it solves the
problem for me ;-)
Regards,
-Janjaap
See:
reverted: commit f81f2f7c9fee307e371f37424577d46f9eaf8692
Author: Tejun Heo <t...@kernel.org>
Date: Tue Apr 28 13:06:10 2009 +0900
ubd: drop unnecessary rq->sector manipulation
ubd curiously updates rq->sector while issuing the request
in multiple pieces. Don't do it and simply use local copy
of sector.
See for original reason:
commit 0a6d3a2a3813e7b25267366cfbf9a4a4698dd1c2
Author: Jeff Dike <jd...@addtoit.com>
Date: Sun Jul 15 23:38:47 2007 -0700
uml: fix request->sector update
It is theoretically possible for a request to finish and be freed
between writing it to the I/O thread and updating the sector count. In
this case, the update will dereference a freed pointer.
To avoid this, I delay the update until processing the next sg
segment, when the request pointer is known to be good.
modified: arch/um/drivers/ubd_kern.c
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