The patch titled
Subject: nbd: support FLUSH requests
has been removed from the -mm tree. Its filename was
nbd-support-flush-requests.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Alex Bligh <alex@xxxxxxxxxxx>
Subject: nbd: support FLUSH requests
Currently, the NBD device does not accept flush requests from the Linux
block layer. If the NBD server opened the target with neither O_SYNC nor
O_DSYNC, however, the device will be effectively backed by a writeback
cache. Without issuing flushes properly, operation of the NBD device will
not be safe against power losses.
The NBD protocol has support for both a cache flush command and a FUA
command flag; the server will also pass a flag to note its support for
these features. This patch adds support for the cache flush command and
flag. In the kernel, we receive the flags via the NBD_SET_FLAGS ioctl,
and map NBD_FLAG_SEND_FLUSH to the argument of blk_queue_flush. When the
flag is active the block layer will send REQ_FLUSH requests, which we
translate to NBD_CMD_FLUSH commands.
FUA support is not included in this patch because all free software
servers implement it with a full fdatasync; thus it has no advantage over
supporting flush only. Because I [Paolo] cannot really benchmark it in a
realistic scenario, I cannot tell if it is a good idea or not. It is also
not clear if it is valid for an NBD server to support FUA but not flush.
The Linux block layer gives a warning for this combination, the NBD
protocol documentation says nothing about it.
The patch also fixes a small problem in the handling of flags: nbd->flags
must be cleared at the end of NBD_DO_IT, but the driver was not doing
that. The bug manifests itself as follows. Suppose you two different
client/server pairs to start the NBD device. Suppose also that the first
client supports NBD_SET_FLAGS, and the first server sends
NBD_FLAG_SEND_FLUSH; the second pair instead does neither of these two
things. Before this patch, the second invocation of NBD_DO_IT will use a
stale value of nbd->flags, and the second server will issue an error every
time it receives an NBD_CMD_FLUSH command.
This bug is pre-existing, but it becomes much more important after this
patch; flush failures make the device pretty much unusable, unlike
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Alex Bligh <alex@xxxxxxxxxxx>
Acked-by: Paul Clements <Paul.Clements@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/block/nbd.c | 22 ++++++++++++++++++++--
include/uapi/linux/nbd.h | 3 ++-
2 files changed, 22 insertions(+), 3 deletions(-)
diff -puN drivers/block/nbd.c~nbd-support-flush-requests drivers/block/nbd.c
--- a/drivers/block/nbd.c~nbd-support-flush-requests
+++ a/drivers/block/nbd.c
@@ -98,6 +98,7 @@ static const char *nbdcmd_to_ascii(int c
case NBD_CMD_READ: return "read";
case NBD_CMD_WRITE: return "write";
case NBD_CMD_DISC: return "disconnect";
+ case NBD_CMD_FLUSH: return "flush";
case NBD_CMD_TRIM: return "trim/discard";
}
return "invalid";
@@ -244,8 +245,15 @@ static int nbd_send_req(struct nbd_devic
request.magic = htonl(NBD_REQUEST_MAGIC);
request.type = htonl(nbd_cmd(req));
- request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9);
- request.len = htonl(size);
+
+ if (nbd_cmd(req) == NBD_CMD_FLUSH) {
+ /* Other values are reserved for FLUSH requests. */
+ request.from = 0;
+ request.len = 0;
+ } else {
+ request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9);
+ request.len = htonl(size);
+ }
memcpy(request.handle, &req, sizeof(req));
dprintk(DBG_TX, "%s: request %p: sending control (%s@%llu,%uB)\n",
@@ -482,6 +490,11 @@ static void nbd_handle_req(struct nbd_de
}
}
+ if (req->cmd_flags & REQ_FLUSH) {
+ BUG_ON(unlikely(blk_rq_sectors(req)));
+ nbd_cmd(req) = NBD_CMD_FLUSH;
+ }
+
req->errors = 0;
mutex_lock(&nbd->tx_lock);
@@ -684,6 +697,10 @@ static int __nbd_ioctl(struct block_devi
if (nbd->flags & NBD_FLAG_SEND_TRIM)
queue_flag_set_unlocked(QUEUE_FLAG_DISCARD,
nbd->disk->queue);
+ if (nbd->flags & NBD_FLAG_SEND_FLUSH)
+ blk_queue_flush(nbd->disk->queue, REQ_FLUSH);
+ else
+ blk_queue_flush(nbd->disk->queue, 0);
thread = kthread_create(nbd_thread, nbd, nbd->disk->disk_name);
if (IS_ERR(thread)) {
@@ -705,6 +722,7 @@ static int __nbd_ioctl(struct block_devi
queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, nbd->disk->queue);
if (file)
fput(file);
+ nbd->flags = 0;
nbd->bytesize = 0;
bdev->bd_inode->i_size = 0;
set_capacity(nbd->disk, 0);
diff -puN include/uapi/linux/nbd.h~nbd-support-flush-requests include/uapi/linux/nbd.h
--- a/include/uapi/linux/nbd.h~nbd-support-flush-requests
+++ a/include/uapi/linux/nbd.h
@@ -33,13 +33,14 @@ enum {
NBD_CMD_READ = 0,
NBD_CMD_WRITE = 1,
NBD_CMD_DISC = 2,
- /* there is a gap here to match userspace */
+ NBD_CMD_FLUSH = 3,
NBD_CMD_TRIM = 4
};
/* values for flags field */
#define NBD_FLAG_HAS_FLAGS (1 << 0) /* nbd-server supports flags */
#define NBD_FLAG_READ_ONLY (1 << 1) /* device is read-only */
+#define NBD_FLAG_SEND_FLUSH (1 << 2) /* can flush writeback cache */
/* there is a gap here to match userspace */
#define NBD_FLAG_SEND_TRIM (1 << 5) /* send trim/discard */
_
Patches currently in -mm which might be from alex@xxxxxxxxxxx are
origin.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
