Hi Linus,
I've got strange idea and tried to build diskless machine around
2.5.3... Besides problem with segfaulting crc32 (it is initialized after
net/ipv4/ipconfig.c due to lib/lib.a being a library... I had to hardcode
lib/crc32.o before --start-group in main Makefile, but it is another
story) there is bad problem with NBD caused by BIO changes:
(1) request flags were immediately put into on-wire request format.
In the past, we had 0=READ, !0=WRITE. Now only REQ_RW bit determines
direction. As nbd-server from nbd distribution package treats any
non-zero value as write, it performs writes instead of read. Fortunately
it will die due to other consistency checks on incoming request, but...
(2) nbd servers handle only up to 10240 byte requests. So setting max_sectors
to 20 is needed, as otherwise nbd server commits suicide. Maximum request size
should be handshaked during nbd initialization, but currently just use
hardwired 20 sectors, so it will behave like it did in the past.
Thanks,
Petr Vandrovec
vandrove@vc.cvut.cz
diff -urdN linux/drivers/block/nbd.c linux/drivers/block/nbd.c
--- linux/drivers/block/nbd.c Thu Jan 10 18:15:38 2002
+++ linux/drivers/block/nbd.c Thu Jan 31 00:24:50 2002
@@ -155,14 +155,15 @@
unsigned long size = req->nr_sectors << 9;
DEBUG("NBD: sending control, ");
+
+ rw = rq_data_dir(req);
+
request.magic = htonl(NBD_REQUEST_MAGIC);
- request.type = htonl(req->flags);
+ request.type = htonl((rw & WRITE) ? 1 : 0);
request.from = cpu_to_be64( (u64) req->sector << 9);
request.len = htonl(size);
memcpy(request.handle, &req, sizeof(req));
- rw = rq_data_dir(req);
-
result = nbd_xmit(1, sock, (char *) &request, sizeof(request), rw & WRITE ? MSG_MORE : 0);
if (result <= 0)
FAIL("Sendmsg failed for control.");
@@ -517,6 +518,7 @@
blksize_size[MAJOR_NR] = nbd_blksizes;
blk_size[MAJOR_NR] = nbd_sizes;
blk_init_queue(BLK_DEFAULT_QUEUE(MAJOR_NR), do_nbd_request, &nbd_lock);
+ blk_queue_max_sectors(BLK_DEFAULT_QUEUE(MAJOR_NR), 20);
for (i = 0; i < MAX_NBD; i++) {
nbd_dev[i].refcnt = 0;
nbd_dev[i].file = NULL;
-
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This archive was generated by hypermail 2b29 : Thu Jan 31 2002 - 21:01:34 EST