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NBD userland client and server have FUA (forced unit access) support
and flags defined. Make NBD kernel module recognize NBD_FLAG_SEND_FUA,
enable FUA on the queue, and forward FUA requests to the server.
Signed-off-by: Shaun McDowell <[email protected]>
Reviewed-by: Josef Bacik <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
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For ease of management it would be nice for users to specify that the
device node for a nbd device is destroyed once it is disconnected and
there are no more users. Add a client flag and enable this operation to
happen.
Signed-off-by: Josef Bacik <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
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Bit #7 is already used, move to bit #8 which is the first unused
one.
Fixes: 9561a7ade0c2 ("nbd: add multi-connection support")
Signed-off-by: Jens Axboe <[email protected]>
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NBD can become contended on its single connection. We have to serialize all
writes and we can only process one read response at a time. Fix this by
allowing userspace to provide multiple connections to a single nbd device. This
coupled with block-mq drastically increases performance in multi-process cases.
Thanks,
Signed-off-by: Josef Bacik <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
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Signed-off-by: Christoph Hellwig <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
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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 <[email protected]>
Signed-off-by: Alex Bligh <[email protected]>
Acked-by: Paul Clements <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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Signed-off-by: David Howells <[email protected]>
Acked-by: Arnd Bergmann <[email protected]>
Acked-by: Thomas Gleixner <[email protected]>
Acked-by: Michael Kerrisk <[email protected]>
Acked-by: Paul E. McKenney <[email protected]>
Acked-by: Dave Jones <[email protected]>
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