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block: Expose block limits for images in QMP

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This information can be useful both for debugging and for management
tools trying to configure guest devices with the optimal limits
(possibly across multiple hosts). There is no reason not to make it
available, so just add it to BlockNodeInfo.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Message-ID: <20251024123041.51254-3-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf 2025-10-24 14:30:38 +02:00
parent 46dd683d56
commit d2634e1828
5 changed files with 102 additions and 14 deletions
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66
qapi/block-core.json
View file

@ -275,6 +275,69 @@
'file': 'ImageInfoSpecificFileWrapper'
} }
##
# @BlockLimitsInfo:
#
# @request-alignment: Alignment requirement, in bytes, for
# offset/length of I/O requests.
#
# @max-discard: Maximum number of bytes that can be discarded at once.
# If not present, there is no specific maximum.
#
# @discard-alignment: Optimal alignment for discard requests in bytes.
# Note that this doesn't have to be a power of two. If not
# present, discards don't have a alignment requirement different
# from @request-alignment.
#
# @max-write-zeroes: Maximum number of bytes that can be zeroed out at
# once. If not present, there is no specific maximum.
#
# @write-zeroes-alignment: Optimal alignment for write zeroes requests
# in bytes. Note that this doesn't have to be a power of two. If
# not present, write_zeroes doesn't have a alignment requirement
# different from @request-alignment.
#
# @opt-transfer: Optimal transfer length in bytes. If not present,
# there is no preferred size.
#
# @max-transfer: Maximal transfer length in bytes. If not present,
# there is no specific maximum.
#
# @max-hw-transfer: Maximal hardware transfer length in bytes.
# Applies whenever transfers to the device bypass the kernel I/O
# scheduler, for example with SG_IO. If not present, there is no
# specific maximum.
#
# @max-iov: Maximum number of scatter/gather elements
#
# @max-hw-iov: Maximum number of scatter/gather elements allowed by
# the hardware. Applies whenever transfers to the device bypass
# the kernel I/O scheduler, for example with SG_IO. If not
# present, the hardware limits is unknown and @max-iov is always
# used.
#
# @min-mem-alignment: Minimal required memory alignment in bytes for
# zero-copy I/O to succeed. For unaligned requests, a bounce
# buffer will be used.
#
# @opt-mem-alignment: Optimal memory alignment in bytes. This is the
# alignment used for any buffer allocations QEMU performs
# internally.
##
{ 'struct': 'BlockLimitsInfo',
'data': { 'request-alignment': 'uint32',
'*max-discard': 'uint64',
'*discard-alignment': 'uint32',
'*max-write-zeroes': 'uint64',
'*write-zeroes-alignment': 'uint32',
'*opt-transfer': 'uint32',
'*max-transfer': 'uint32',
'*max-hw-transfer': 'uint32',
'max-iov': 'int',
'*max-hw-iov': 'int',
'min-mem-alignment': 'size',
'opt-mem-alignment': 'size' } }
##
# @BlockNodeInfo:
#
@ -304,6 +367,8 @@
#
# @snapshots: list of VM snapshots
#
# @limits: block limits that are used for I/O on the node (Since 10.2)
#
# @format-specific: structure supplying additional format-specific
# information (since 1.7)
#
@ -315,6 +380,7 @@
'*cluster-size': 'int', '*encrypted': 'bool', '*compressed': 'bool',
'*backing-filename': 'str', '*full-backing-filename': 'str',
'*backing-filename-format': 'str', '*snapshots': ['SnapshotInfo'],
'*limits': 'BlockLimitsInfo',
'*format-specific': 'ImageInfoSpecific' } }
##