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Subject[patch 1/3] uml-ubd-no-empty-queue
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Avoid using, in the UBD driver, the elv_queue_empty function. It's for
the block layer only; in fact, the Anticipatory Scheduler can return NULL
with elv_next_request() even if the queue is not empty, because it waits
for the process to send another request before seeking on the disk.

In fact, if (with uml-ubd-any-elevator) we let UBD use any scheduler,
elevator=as will make the UBD driver Oops, if we don't have this patch.
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade_spam@yahoo.it>
---
uml-linux-2.6.8.1-paolo/arch/um/drivers/ubd_kern.c | 6 ++----
1 files changed, 2 insertions(+), 4 deletions(-)
diff -puN arch/um/drivers/ubd_kern.c~uml-ubd-no-empty-queue arch/um/drivers/ubd_kern.c
--- uml-linux-2.6.8.1/arch/um/drivers/ubd_kern.c~uml-ubd-no-empty-queue 2004-08-29 14:40:51.313410952 +0200
+++ uml-linux-2.6.8.1-paolo/arch/um/drivers/ubd_kern.c 2004-08-29 14:40:51.315410648 +0200
@@ -1038,8 +1038,7 @@ static void do_ubd_request(request_queue
int err, n;

if(thread_fd == -1){
- while(!elv_queue_empty(q)){
- req = elv_next_request(q);
+ while((req = elv_next_request(q)) != NULL){
err = prepare_request(req, &io_req);
if(!err){
do_io(&io_req);
@@ -1048,9 +1047,8 @@ static void do_ubd_request(request_queue
}
}
else {
- if(do_ubd || elv_queue_empty(q))
+ if(do_ubd || (req = elv_next_request(q)) == NULL)
return;
- req = elv_next_request(q);
err = prepare_request(req, &io_req);
if(!err){
do_ubd = ubd_handler;
_
-
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