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01b05c66a3
qemu/nbd
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Eric Blake 01b05c66a3 nbd/client: Don't hard-disconnect on ESHUTDOWN from server 
The NBD spec says that a server may fail any transmission request
with ESHUTDOWN when it is apparent that no further request from
the client can be successfully honored.  The client is supposed
to then initiate a soft shutdown (wait for all remaining in-flight
requests to be answered, then send NBD_CMD_DISC).  However, since
qemu's server never uses ESHUTDOWN errors, this code was mostly
untested since its introduction in commit b6f5d3b5.

More recently, I learned that nbdkit as the NBD server is able to
send ESHUTDOWN errors, so I finally tested this code, and noticed
that our client was special-casing ESHUTDOWN to cause a hard
shutdown (immediate disconnect, with no NBD_CMD_DISC), but only
if the server sends this error as a simple reply.  Further
investigation found that commit d2febedb introduced a regression
where structured replies behave differently than simple replies -
but that the structured reply behavior is more in line with the
spec (even if we still lack code in nbd-client.c to properly quit
sending further requests).  So this patch reverts the portion of
b6f5d3b5 that introduced an improper hard-disconnect special-case
at the lower level, and leaves the future enhancement of a nicer
soft-disconnect at the higher level for another day.

CC: qemu-stable@nongnu.org
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20171113194857.13933-1-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
2017-11-17 08:34:34 -06:00
..
client.c nbd/client: Don't hard-disconnect on ESHUTDOWN from server 2017-11-17 08:34:34 -06:00
common.c nbd: Expose constants and structs for structured read 2017-10-30 21:07:21 +01:00
Makefile.objs nbd: Split nbd.c 2016-01-15 18:58:02 +01:00
nbd-internal.h nbd: Minimal structured read for client 2017-10-30 21:48:41 +01:00
server.c nbd/server: Fix structured read of length 0 2017-11-09 10:25:11 -06:00
trace-events nbd/server: Fix structured read of length 0 2017-11-09 10:25:11 -06:00