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Block layer patches:
- qcow2: Support for external data files - qcow2: Default to 4KB for the qcow2 cache entry size - Apply block driver whitelist for -drive format=help - Several qemu-iotests improvements -----BEGIN PGP SIGNATURE----- iQIcBAABAgAGBQJcgmYDAAoJEH8JsnLIjy/WiEgP/jirn5n4bFHDSzpofRxgpcEG 2SoBpYtJQvAVgXmg8P1ZKeaX5yiiZpJS475ShuH6C3dnWuaHBBjvQfDkLLrh3v05 4KJyZQUFx0WQZqkEiHxtgmE3iIOAsWe8VzBCZjsFITdp+fN8HlRjKVofyYP0y48G k9PzMlEe30Wu2s+lq6PEIXgpwIZqOVl1V3C7wDF8Vg/1OOsv+rK0vKD8yra/oQAc mthM+hjkpa+ohjE5aTeCsDVxO56AStvXv0d3bE0aF/ZtCvQdbVh5coYj1ldNz6VY Bvx+UP7kPHJw0wesZJXLeVyZUMyHAuu9vW6zKlDYJ7PoIXSLXC7rYyoEofvkAzQL awSluFj4HpYU1dKseJ8LzrMyUqjJ2eLJ+K48iNIh0vNlVuvX8aR62dIv0Obo3rod Y7zgyd6mSgDGulDa3xVsD0+eAUUEbLaUDBV80+M7S2/V9YP4Bt7lKbm0SQB4dUxm eOJfnbMTpIYUUjYtpCkURED3MlTIA51fy28O87TMJwa11sJTXRscysE9oNQNsvwW 2UPhMPLykMI023glhV0vCwgXQ5kktOvpaB3U7LGQhhHd1ed9sdLEB1bO9eKWYr4N h6QPLBRLGUYd+BFMMIBLQtx8r+mAn1hUZoX4zxTn0lD50Rch3pRnCjMoC1iWqRkS J204Lzum5kgNPheyVxhy =GCRI -----END PGP SIGNATURE----- Merge remote-tracking branch 'remotes/kevin/tags/for-upstream' into staging Block layer patches: - qcow2: Support for external data files - qcow2: Default to 4KB for the qcow2 cache entry size - Apply block driver whitelist for -drive format=help - Several qemu-iotests improvements # gpg: Signature made Fri 08 Mar 2019 12:54:27 GMT # gpg: using RSA key 7F09B272C88F2FD6 # gpg: Good signature from "Kevin Wolf <kwolf@redhat.com>" [full] # Primary key fingerprint: DC3D EB15 9A9A F95D 3D74 56FE 7F09 B272 C88F 2FD6 * remotes/kevin/tags/for-upstream: (33 commits) qcow2 spec: Describe string header extensions qemu-iotests: Add dependency to qemu-nbd tool ahci-test: Add dependency to qemu-img tool qemu-iotests: amend with external data file qemu-iotests: General tests for qcow2 with external data file qemu-iotests: Preallocation with external data file qcow2: Implement data-file-raw create option qcow2: Store data file name in the image qcow2: Creating images with external data file qcow2: Add basic data-file infrastructure qcow2: Support external data file in qemu-img check qcow2: Return error for snapshot operation with data file qcow2: External file I/O qcow2: Prepare qcow2_co_block_status() for data file qcow2: Return 0/-errno in qcow2_alloc_compressed_cluster_offset() qcow2: Don't assume 0 is an invalid cluster offset qcow2: Prepare count_contiguous_clusters() for external data file qcow2: Prepare qcow2_get_cluster_type() for external data file qcow2: Pass bs to qcow2_get_cluster_type() qcow2: Basic definitions for external data files ... Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Peter Maydell
commit
4c76137484
215 changed files with 1583 additions and 421 deletions
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@ -97,7 +97,19 @@ in the description of a field.
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be written to (unless for regaining
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consistency).
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Bits 2-63: Reserved (set to 0)
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Bit 2: External data file bit. If this bit is set, an
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external data file is used. Guest clusters are
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then stored in the external data file. For such
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images, clusters in the external data file are
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not refcounted. The offset field in the
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Standard Cluster Descriptor must match the
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guest offset and neither compressed clusters
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nor internal snapshots are supported.
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An External Data File Name header extension may
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be present if this bit is set.
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Bits 3-63: Reserved (set to 0)
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80 - 87: compatible_features
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Bitmask of compatible features. An implementation can
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@ -126,7 +138,21 @@ in the description of a field.
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bit is unset, the bitmaps extension data must be
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considered inconsistent.
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Bits 1-63: Reserved (set to 0)
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Bit 1: If this bit is set, the external data file can
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be read as a consistent standalone raw image
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without looking at the qcow2 metadata.
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Setting this bit has a performance impact for
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some operations on the image (e.g. writing
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zeros requires writing to the data file instead
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of only setting the zero flag in the L2 table
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entry) and conflicts with backing files.
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This bit may only be set if the External Data
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File bit (incompatible feature bit 1) is also
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set.
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Bits 2-63: Reserved (set to 0)
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96 - 99: refcount_order
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Describes the width of a reference count block entry (width
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@ -144,10 +170,11 @@ be stored. Each extension has a structure like the following:
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Byte 0 - 3: Header extension type:
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0x00000000 - End of the header extension area
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0xE2792ACA - Backing file format name
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0xE2792ACA - Backing file format name string
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0x6803f857 - Feature name table
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0x23852875 - Bitmaps extension
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0x0537be77 - Full disk encryption header pointer
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0x44415441 - External data file name string
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other - Unknown header extension, can be safely
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ignored
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@ -169,6 +196,16 @@ data of compatible features that it doesn't support. Compatible features that
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need space for additional data can use a header extension.
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== String header extensions ==
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Some header extensions (such as the backing file format name and the external
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data file name) are just a single string. In this case, the header extension
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length is the string length and the string is not '\0' terminated. (The header
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extension padding can make it look like a string is '\0' terminated, but
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neither is padding always necessary nor is there a guarantee that zero bytes
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are used for padding.)
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== Feature name table ==
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The feature name table is an optional header extension that contains the name
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@ -437,6 +474,11 @@ L2 table entry:
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This information is only accurate in L2 tables
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that are reachable from the active L1 table.
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With external data files, all guest clusters have an
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implicit refcount of 1 (because of the fixed host = guest
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mapping for guest cluster offsets), so this bit should be 1
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for all allocated clusters.
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Standard Cluster Descriptor:
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Bit 0: If set to 1, the cluster reads as all zeros. The host
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@ -450,8 +492,10 @@ Standard Cluster Descriptor:
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1 - 8: Reserved (set to 0)
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9 - 55: Bits 9-55 of host cluster offset. Must be aligned to a
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cluster boundary. If the offset is 0, the cluster is
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unallocated.
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cluster boundary. If the offset is 0 and bit 63 is clear,
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the cluster is unallocated. The offset may only be 0 with
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bit 63 set (indicating a host cluster offset of 0) when an
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external data file is used.
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56 - 61: Reserved (set to 0)
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@ -158,10 +158,10 @@ refcount cache is as small as possible unless overridden by the user.
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Using smaller cache entries
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---------------------------
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The qcow2 L2 cache stores complete tables by default. This means that
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if QEMU needs an entry from an L2 table then the whole table is read
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from disk and is kept in the cache. If the cache is full then a
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complete table needs to be evicted first.
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The qcow2 L2 cache can store complete tables. This means that if QEMU
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needs an entry from an L2 table then the whole table is read from disk
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and is kept in the cache. If the cache is full then a complete table
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needs to be evicted first.
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This can be inefficient with large cluster sizes since it results in
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more disk I/O and wastes more cache memory.
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@ -172,6 +172,9 @@ it smaller than the cluster size. This can be configured using the
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-drive file=hd.qcow2,l2-cache-size=2097152,l2-cache-entry-size=4096
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Since QEMU 4.0 the value of l2-cache-entry-size defaults to 4KB (or
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the cluster size if it's smaller).
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Some things to take into account:
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- The L2 cache entry size has the same restrictions as the cluster
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@ -185,7 +188,8 @@ Some things to take into account:
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- Try different entry sizes to see which one gives faster performance
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in your case. The block size of the host filesystem is generally a
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good default (usually 4096 bytes in the case of ext4).
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good default (usually 4096 bytes in the case of ext4, hence the
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default).
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- Only the L2 cache can be configured this way. The refcount cache
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always uses the cluster size as the entry size.
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@ -194,7 +198,8 @@ Some things to take into account:
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(as explained in the "Choosing the right cache sizes" and "How to
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configure the cache sizes" sections in this document) then none of
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this is necessary and you can omit the "l2-cache-entry-size"
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parameter altogether.
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parameter altogether. In this case QEMU makes the entry size
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equal to the cluster size by default.
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Reducing the memory usage
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