The upstream NBD Protocol has defined a new extension to allow
the server to advertise block sizes to the client, as well as
a way for the client to inform the server whether it intends to
obey block sizes.
When using the block layer as the client, we will obey block
sizes; but when used as 'qemu-nbd -c' to hand off to the
kernel nbd module as the client, we are still waiting for the
kernel to implement a way for us to learn if it will honor
block sizes (perhaps by an addition to sysfs, rather than an
ioctl), as well as any way to tell the kernel what additional
block sizes to obey (NBD_SET_BLKSIZE appears to be accurate
for the minimum size, but preferred and maximum sizes would
probably be new ioctl()s), so until then, we need to make our
request for block sizes conditional.
When using ioctl(NBD_SET_BLKSIZE) to hand off to the kernel,
use the minimum block size as the sector size if it is larger
than 512, which also has the nice effect of cooperating with
(non-qemu) servers that don't do read-modify-write when
exposing a block device with 4k sectors; it might also allow
us to visit a file larger than 2T on a 32-bit kernel.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20170707203049.534-10-eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The upstream NBD Protocol has defined a new extension to allow
the server to advertise block sizes to the client, as well as
a way for the client to inform the server that it intends to
obey block sizes.
Thanks to a recent fix (commit df7b97ff), our real minimum
transfer size is always 1 (the block layer takes care of
read-modify-write on our behalf), but we're still more efficient
if we advertise 512 when the client supports it, as follows:
- OPT_INFO, but no NBD_INFO_BLOCK_SIZE: advertise 512, then
fail with NBD_REP_ERR_BLOCK_SIZE_REQD; client is free to try
something else since we don't disconnect
- OPT_INFO with NBD_INFO_BLOCK_SIZE: advertise 512
- OPT_GO, but no NBD_INFO_BLOCK_SIZE: advertise 1
- OPT_GO with NBD_INFO_BLOCK_SIZE: advertise 512
We can also advertise the optimum block size (presumably the
cluster size, when exporting a qcow2 file), and our absolute
maximum transfer size of 32M, to help newer clients avoid
EINVAL failures or abrupt disconnects on oversize requests.
We do not reject clients for using the older NBD_OPT_EXPORT_NAME;
we are no worse off for those clients than we used to be.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20170707203049.534-9-eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
NBD_OPT_EXPORT_NAME is lousy: per the NBD protocol, any failure
requires the server to close the connection rather than report an
error to us. Therefore, upstream NBD recently added NBD_OPT_GO as
the improved version of the option that does what we want [1]: it
reports sane errors on failures, and on success provides at least
as much info as NBD_OPT_EXPORT_NAME.
[1] https://github.com/NetworkBlockDevice/nbd/blob/extension-info/doc/proto.md
This is a first cut at use of the information types. Note that we
do not need to use NBD_OPT_INFO, and that use of NBD_OPT_GO means
we no longer have to use NBD_OPT_LIST to learn whether a server
requires TLS (this requires servers that gracefully handle unknown
NBD_OPT, many servers prior to qemu 2.5 were buggy, but I have patched
qemu, upstream nbd, and nbdkit in the meantime, in part because of
interoperability testing with this patch). We still fall back to
NBD_OPT_LIST when NBD_OPT_GO is not supported on the server, as it
is still one last chance for a nicer error message. Later patches
will use further info, like NBD_INFO_BLOCK_SIZE.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20170707203049.534-8-eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
NBD_OPT_EXPORT_NAME is lousy: per the NBD protocol, any failure
requires us to close the connection rather than report an error.
Therefore, upstream NBD recently added NBD_OPT_GO as the improved
version of the option that does what we want [1], along with
NBD_OPT_INFO that returns the same information but does not
transition to transmission phase.
[1] https://github.com/NetworkBlockDevice/nbd/blob/extension-info/doc/proto.md
This is a first cut at the information types, and only passes the
same information already available through NBD_OPT_LIST and
NBD_OPT_EXPORT_NAME; items like NBD_INFO_BLOCK_SIZE (and thus any
use of NBD_REP_ERR_BLOCK_SIZE_REQD) are intentionally left for
later patches.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20170707203049.534-7-eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Simplify the tracing of client flags in the server, and return -EINVAL
instead of -EIO if we successfully read but don't like those flags.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20170707203049.534-5-eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The NBD protocol has several constants defined in various extensions
that we are about to implement. Expose them to the code, along with
an easy way to map various constants to strings during diagnostic
messages.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20170707203049.534-4-eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
We really don't care if our spec-compliant reply to NBD_OPT_ABORT
was received, so shave off some lines of code by not even tracing it.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20170707203049.534-3-eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Let NBD use the trace mechanisms already present in qemu. Now you can
use the -trace optino of qemu, or the -T/--trace option of qemu-img,
qemu-io, and qemu-nbd, to select nbd traces. For qemu, the QMP commands
trace-event-{get,set}-state can also toggle tracing on the fly.
Example:
qemu-nbd --trace 'nbd_*' <image file> # enables all nbd traces
Recompilation with CFLAGS=-DDEBUG_NBD is no more needed, furthermore,
DEBUG_NBD macro is removed from the code.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20170707152918.23086-11-vsementsov@virtuozzo.com>
[eblake: minor tweaks to a couple of traces]
Signed-off-by: Eric Blake <eblake@redhat.com>
