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b0245d6478
Both NBD_CMD_BLOCK_STATUS and structured NBD_CMD_READ will split their reply according to bdrv_block_status() boundaries. If the block device has a request_alignment smaller than 512, but we advertise a block alignment of 512 to the client, then this can result in the server reply violating client expectations by reporting a smaller region of the export than what the client is permitted to address (although this is less of an issue for qemu 4.0 clients, given recent client patches to overlook our non-compliance at EOF). Since it's always better to be strict in what we send, it is worth advertising the actual minimum block limit rather than blindly rounding it up to 512. Note that this patch is not foolproof - it is still possible to provoke non-compliant server behavior using: $ qemu-nbd --image-opts driver=blkdebug,align=512,image.driver=file,image.filename=/path/to/non-aligned-file That is arguably a bug in the blkdebug driver (it should never pass back block status smaller than its alignment, even if it has to make multiple bdrv_get_status calls and determine the least-common-denominator status among the group to return). It may also be possible to observe issues with a backing layer with smaller alignment than the active layer, although so far I have been unable to write a reliable iotest for that scenario (but again, an issue like that could be argued to be a bug in the block layer, or something where we need a flag to bdrv_block_status() to state whether the result must be aligned to the current layer's limits or can be subdivided for accuracy when chasing backing files). Anyways, as blkdebug is not normally used, and as this patch makes our server more interoperable with qemu 3.1 clients, it is worth applying now, even while we still work on a larger patch series for the 4.1 timeframe to have byte-accurate file lengths. Note that the iotests output changes - for 223 and 233, we can see the server's better granularity advertisement; and for 241, the three test cases have the following effects: - natural alignment: the server's smaller alignment is now advertised, and the hole reported at EOF is now the right result; we've gotten rid of the server's non-compliance - forced server alignment: the server still advertises 512 bytes, but still sends a mid-sector hole. This is still a server compliance bug, which needs to be fixed in the block layer in a later patch; output does not change because the client is already being tolerant of the non-compliance - forced client alignment: the server's smaller alignment means that the client now sees the server's status change mid-sector without any protocol violations, but the fact that the map shows an unaligned mid-sector hole is evidence of the block layer problems with aligned block status, to be fixed in a later patch Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <20190329042750.14704-7-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> [eblake: rebase to enhanced iotest 241 coverage]
104 lines
4.2 KiB
Plaintext
104 lines
4.2 KiB
Plaintext
QA output created by 223
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=== Create partially sparse image, then add dirty bitmaps ===
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=4194304
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wrote 2097152/2097152 bytes at offset 1048576
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2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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Testing:
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QMP_VERSION
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{"return": {}}
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{"return": {}}
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{"return": {}}
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{"return": {}}
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{"return": {}}
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{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "SHUTDOWN", "data": {"guest": false, "reason": "host-qmp-quit"}}
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=== Write part of the file under active bitmap ===
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wrote 512/512 bytes at offset 512
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512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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wrote 2097152/2097152 bytes at offset 2097152
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2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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=== End dirty bitmaps, and start serving image over NBD ===
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{"return": {}}
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{"return": {}}
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{"return": {}}
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{"error": {"class": "GenericError", "desc": "NBD server not running"}}
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{"return": {}}
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{"error": {"class": "GenericError", "desc": "NBD server already running"}}
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exports available: 0
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{"return": {}}
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{"error": {"class": "GenericError", "desc": "Cannot find device=nosuch nor node_name=nosuch"}}
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{"error": {"class": "GenericError", "desc": "NBD server already has export named 'n'"}}
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{"error": {"class": "GenericError", "desc": "Enabled bitmap 'b2' incompatible with readonly export"}}
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{"error": {"class": "GenericError", "desc": "Bitmap 'b3' is not found"}}
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{"return": {}}
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exports available: 2
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export: 'n'
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size: 4194304
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flags: 0x4ef ( readonly flush fua trim zeroes df cache )
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min block: 1
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opt block: 4096
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max block: 33554432
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available meta contexts: 2
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base:allocation
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qemu:dirty-bitmap:b
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export: 'n2'
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size: 4194304
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flags: 0x4ed ( flush fua trim zeroes df cache )
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min block: 1
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opt block: 4096
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max block: 33554432
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available meta contexts: 2
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base:allocation
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qemu:dirty-bitmap:b2
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=== Contrast normal status to large granularity dirty-bitmap ===
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read 512/512 bytes at offset 512
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512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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read 524288/524288 bytes at offset 524288
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512 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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read 1048576/1048576 bytes at offset 1048576
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1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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read 2097152/2097152 bytes at offset 2097152
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2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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[{ "start": 0, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
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{ "start": 4096, "length": 1044480, "depth": 0, "zero": true, "data": false, "offset": OFFSET},
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{ "start": 1048576, "length": 3145728, "depth": 0, "zero": false, "data": true, "offset": OFFSET}]
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[{ "start": 0, "length": 65536, "depth": 0, "zero": false, "data": false},
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{ "start": 65536, "length": 2031616, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
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{ "start": 2097152, "length": 2097152, "depth": 0, "zero": false, "data": false}]
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=== Contrast to small granularity dirty-bitmap ===
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[{ "start": 0, "length": 512, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
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{ "start": 512, "length": 512, "depth": 0, "zero": false, "data": false},
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{ "start": 1024, "length": 2096128, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
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{ "start": 2097152, "length": 2097152, "depth": 0, "zero": false, "data": false}]
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=== End qemu NBD server ===
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{"return": {}}
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{"return": {}}
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{"error": {"class": "GenericError", "desc": "Export 'n2' is not found"}}
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{"return": {}}
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{"error": {"class": "GenericError", "desc": "NBD server not running"}}
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{"return": {}}
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{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "SHUTDOWN", "data": {"guest": false, "reason": "host-qmp-quit"}}
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=== Use qemu-nbd as server ===
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[{ "start": 0, "length": 65536, "depth": 0, "zero": false, "data": false},
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{ "start": 65536, "length": 2031616, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
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{ "start": 2097152, "length": 2097152, "depth": 0, "zero": false, "data": false}]
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[{ "start": 0, "length": 512, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
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{ "start": 512, "length": 512, "depth": 0, "zero": false, "data": false},
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{ "start": 1024, "length": 2096128, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
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{ "start": 2097152, "length": 2097152, "depth": 0, "zero": false, "data": false}]
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*** done
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