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SubjectNBD Fix (attempt #2)
Date
Hi,

Below is a patch which I think fixes the NBD hangs properly. It works for
me and doesn't need any changes to ll_rw_blk.c like my last patch did. I've
shown it to Pavel Machek who has approved it. The patch is against 2.4.2-ac18.

Pavel: I've made the change you requested and also added a flag I forgot before.
Alan: Please apply this patch to your kernel tree.

If memory serves correctly the MSG_MORE flag only appeared in 2.4.2-ac and
isn't in the standard 2.4.2 kernel so I'll prepare a separate patch for
2.4.2 if there are no plans to merge the ZC patches for a while. Is there
a timescale for this or some criteria by which the ZC changes will be judged
ready for merging ?

The one other change which might be required is a userland change. The
buffer size used for I/O by the nbd-server program is not large enough
in the case that a lot of buffers get merged into a single request, this
is easy to change though. If you get a message in your syslog on your
server machine complaining of a request thats too large, then this is
what has happened,

Steve.

------------------------------------------------------------------------------
diff -r -u linux-2.4.2-ac18/drivers/block/nbd.c linux/drivers/block/nbd.c
--- linux-2.4.2-ac18/drivers/block/nbd.c Sun Mar 11 21:35:14 2001
+++ linux/drivers/block/nbd.c Sun Mar 11 20:18:36 2001
@@ -26,7 +26,6 @@
* structure with userland
*/

-#undef NBD_PLUGGABLE
#define PARANOIA
#include <linux/major.h>

@@ -68,8 +67,6 @@
static int requests_out;
#endif

-static void nbd_plug_device(request_queue_t *q, kdev_t dev) { }
-
static int nbd_open(struct inode *inode, struct file *file)
{
int dev;
@@ -88,7 +85,7 @@
/*
* Send or receive packet.
*/
-static int nbd_xmit(int send, struct socket *sock, char *buf, int size)
+static int nbd_xmit(int send, struct socket *sock, char *buf, int size, int msg_flags)
{
mm_segment_t oldfs;
int result;
@@ -118,7 +115,7 @@
msg.msg_control = NULL;
msg.msg_controllen = 0;
msg.msg_namelen = 0;
- msg.msg_flags = 0;
+ msg.msg_flags = msg_flags | MSG_NOSIGNAL;

if (send)
result = sock_sendmsg(sock, &msg, size);
@@ -151,7 +148,7 @@
{
int result;
struct nbd_request request;
- unsigned long size = req->current_nr_sectors << 9;
+ unsigned long size = req->nr_sectors << 9;

DEBUG("NBD: sending control, ");
request.magic = htonl(NBD_REQUEST_MAGIC);
@@ -160,15 +157,19 @@
request.len = htonl(size);
memcpy(request.handle, &req, sizeof(req));

- result = nbd_xmit(1, sock, (char *) &request, sizeof(request));
+ result = nbd_xmit(1, sock, (char *) &request, sizeof(request), req->cmd == WRITE ? MSG_MORE : 0);
if (result <= 0)
FAIL("Sendmsg failed for control.");

if (req->cmd == WRITE) {
+ struct buffer_head *bh = req->bh;
DEBUG("data, ");
- result = nbd_xmit(1, sock, req->buffer, size);
- if (result <= 0)
- FAIL("Send data failed.");
+ do {
+ result = nbd_xmit(1, sock, bh->b_data, bh->b_size, bh->b_reqnext == NULL ? 0 : MSG_MORE);
+ if (result <= 0)
+ FAIL("Send data failed.");
+ bh = bh->b_reqnext;
+ } while(bh);
}
return;

@@ -186,7 +187,7 @@

DEBUG("reading control, ");
reply.magic = 0;
- result = nbd_xmit(0, lo->sock, (char *) &reply, sizeof(reply));
+ result = nbd_xmit(0, lo->sock, (char *) &reply, sizeof(reply), MSG_WAITALL);
if (result <= 0)
HARDFAIL("Recv control failed.");
memcpy(&xreq, reply.handle, sizeof(xreq));
@@ -201,10 +202,14 @@
if (ntohl(reply.error))
FAIL("Other side returned error.");
if (req->cmd == READ) {
+ struct buffer_head *bh = req->bh;
DEBUG("data, ");
- result = nbd_xmit(0, lo->sock, req->buffer, req->current_nr_sectors << 9);
- if (result <= 0)
- HARDFAIL("Recv data failed.");
+ do {
+ result = nbd_xmit(0, lo->sock, bh->b_data, bh->b_size, MSG_WAITALL);
+ if (result <= 0)
+ HARDFAIL("Recv data failed.");
+ bh = bh->b_reqnext;
+ } while(bh);
}
DEBUG("done.\n");
return req;
@@ -218,7 +223,6 @@
void nbd_do_it(struct nbd_device *lo)
{
struct request *req;
- int dequeued;

down (&lo->queue_lock);
while (1) {
@@ -246,11 +250,9 @@
list_del(&req->queue);
up (&lo->queue_lock);

- dequeued = nbd_end_request(req);
+ nbd_end_request(req);

down (&lo->queue_lock);
- if (!dequeued)
- list_add(&req->queue, &lo->queue_head);
}
out:
up (&lo->queue_lock);
@@ -259,7 +261,6 @@
void nbd_clear_que(struct nbd_device *lo)
{
struct request *req;
- int dequeued;

#ifdef PARANOIA
if (lo->magic != LO_MAGIC) {
@@ -284,11 +285,9 @@
list_del(&req->queue);
up(&lo->queue_lock);

- dequeued = nbd_end_request(req);
+ nbd_end_request(req);

down(&lo->queue_lock);
- if (!dequeued)
- list_add(&req->queue, &lo->queue_head);
}
}

@@ -498,9 +497,6 @@
blksize_size[MAJOR_NR] = nbd_blksizes;
blk_size[MAJOR_NR] = nbd_sizes;
blk_init_queue(BLK_DEFAULT_QUEUE(MAJOR_NR), do_nbd_request);
-#ifndef NBD_PLUGGABLE
- blk_queue_pluggable(BLK_DEFAULT_QUEUE(MAJOR_NR), nbd_plug_device);
-#endif
blk_queue_headactive(BLK_DEFAULT_QUEUE(MAJOR_NR), 0);
for (i = 0; i < MAX_NBD; i++) {
nbd_dev[i].refcnt = 0;
diff -r -u linux-2.4.2-ac18/include/linux/blk.h linux/include/linux/blk.h
--- linux-2.4.2-ac18/include/linux/blk.h Sun Mar 11 21:35:17 2001
+++ linux/include/linux/blk.h Sun Mar 11 20:20:08 2001
@@ -42,7 +42,6 @@
extern int swimiop_init(void);
extern int amiga_floppy_init(void);
extern int atari_floppy_init(void);
-extern int nbd_init(void);
extern int ez_init(void);
extern int bpcd_init(void);
extern int ps2esdi_init(void);
diff -r -u linux-2.4.2-ac18/include/linux/nbd.h linux/include/linux/nbd.h
--- linux-2.4.2-ac18/include/linux/nbd.h Mon Dec 11 20:50:42 2000
+++ linux/include/linux/nbd.h Sun Mar 11 20:23:48 2001
@@ -31,35 +31,27 @@
extern int requests_out;
#endif

-static int
+static void
nbd_end_request(struct request *req)
{
+ struct buffer_head *bh;
+ unsigned nsect;
unsigned long flags;
- int ret = 0;
+ int uptodate = (req->errors == 0) ? 1 : 0;

#ifdef PARANOIA
requests_out++;
#endif
- /*
- * This is a very dirty hack that we have to do to handle
- * merged requests because end_request stuff is a bit
- * broken. The fact we have to do this only if there
- * aren't errors looks even more silly.
- */
- if (!req->errors) {
- req->sector += req->current_nr_sectors;
- req->nr_sectors -= req->current_nr_sectors;
- }
-
spin_lock_irqsave(&io_request_lock, flags);
- if (end_that_request_first( req, !req->errors, "nbd" ))
- goto out;
- ret = 1;
- end_that_request_last( req );
-
-out:
+ while((bh = req->bh) != NULL) {
+ nsect = bh->b_size >> 9;
+ blk_finished_io(nsect);
+ req->bh = bh->b_reqnext;
+ bh->b_reqnext = NULL;
+ bh->b_end_io(bh, uptodate);
+ }
+ blkdev_release_request(req);
spin_unlock_irqrestore(&io_request_lock, flags);
- return ret;
}

#define MAX_NBD 128
-
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