use FALLOC_FL_ZERO_RANGE for write_zeroes #109
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The latest implementation from crosvm is preferred. Then the virtio-blk driver chooses to call punch_hole() or write_zeroes_at() according to the |
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That's how I was seeing it too, thanks! I'll open a PR with the switch. |
lauralt
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Nov 19, 2020
Switched to the latest crosvm `write_zeroes` (commit f4a260d) which uses FALLOC_FL_ZERO_RANGE instead of FALLOC_FL_PUNCH_HOLE for writing zeroes to a file. It also adds a new trait, `WriteZeroesAt`, which lets you give the offset in file instead of using the current cursor. This trait allows doing custom implementations for write_zeroes ops too. There is also a new function, write_zeroes_all(), that allows write_zeroes() implementations that don't necessarily fulfill the entire requested length. Fixes: rust-vmm#109. Also added more tests to this module. I'd say this fixes rust-vmm#98 too since making fallocate() actually fail such that some bytes will be written in the fallback option doesn't seem possible to achieve. Signed-off-by: Laura Loghin <lauralg@amazon.com>
lauralt
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Nov 19, 2020
Switched to the latest crosvm `write_zeroes` (commit f4a260d) which uses FALLOC_FL_ZERO_RANGE instead of FALLOC_FL_PUNCH_HOLE for writing zeroes to a file. It also adds a new trait, `WriteZeroesAt`, which lets you give the offset in file instead of using the current cursor. This trait allows doing custom implementations for write_zeroes ops too. There is also a new function, write_zeroes_all(), that allows write_zeroes() implementations that don't necessarily fulfill the entire requested length. Fixes: rust-vmm#109. Also added more tests to this module. I'd say this fixes rust-vmm#98 too since making fallocate() actually fail such that some bytes will be written in the fallback option doesn't seem possible to achieve. Signed-off-by: Laura Loghin <lauralg@amazon.com>
lauralt
added a commit
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Nov 20, 2020
Switched to the latest crosvm `write_zeroes` (commit f4a260d) which uses FALLOC_FL_ZERO_RANGE instead of FALLOC_FL_PUNCH_HOLE for writing zeroes to a file. It also adds a new trait, `WriteZeroesAt`, which lets you give the offset in file instead of using the current cursor. This trait allows doing custom implementations for write_zeroes ops too. There is also a new function, write_all_zeroes(), that allows write_zeroes() implementations that don't necessarily fulfill the entire requested length. Fixes: rust-vmm#109. Also added more tests to this module. I'd say this fixes rust-vmm#98 too since making fallocate() actually fail such that some bytes will be written in the fallback option doesn't seem possible to achieve in unit tests. Signed-off-by: Laura Loghin <lauralg@amazon.com>
lauralt
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Nov 23, 2020
Switched to the latest crosvm `write_zeroes` (commit f4a260d) which uses FALLOC_FL_ZERO_RANGE instead of FALLOC_FL_PUNCH_HOLE for writing zeroes to a file. It also adds a new trait, `WriteZeroesAt`, which lets you give the offset in file instead of using the current cursor. This trait allows doing custom implementations for write_zeroes ops too. There is also a new function, write_all_zeroes(), that allows write_zeroes() implementations that don't necessarily fulfill the entire requested length. Fixes: rust-vmm#109. Also added more tests to this module. I'd say this fixes rust-vmm#98 too since making fallocate() actually fail such that some bytes will be written in the fallback option doesn't seem possible to achieve in unit tests. Signed-off-by: Laura Loghin <lauralg@amazon.com>
lauralt
added a commit
to lauralt/vmm-sys-util
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Nov 23, 2020
Switched to the latest crosvm `write_zeroes` (commit f4a260d) which uses FALLOC_FL_ZERO_RANGE instead of FALLOC_FL_PUNCH_HOLE for writing zeroes to a file. It also adds a new trait, `WriteZeroesAt`, which lets you give the offset in file instead of using the current cursor. This trait allows doing custom implementations for write_zeroes ops too. There is also a new function, write_all_zeroes(), that allows write_zeroes() implementations that don't necessarily fulfill the entire requested length. Fixes: rust-vmm#109. Also added more tests to this module. I'd say this fixes rust-vmm#98 too since making fallocate() actually fail such that some bytes will be written in the fallback option doesn't seem possible to achieve in unit tests. Signed-off-by: Laura Loghin <lauralg@amazon.com>
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While working on the virtio block discard/write_zeroes implementation, I noticed that
write_zeroes()is usingfallocatewith FALLOC_FL_PUNCH_HOLE mode instead of FALLOC_FL_ZERO_RANGE. From the virtio specificationit makes sense to use FALLOC_FL_PUNCH_HOLE for write zeroes request only if
unmapbit is also set, otherwise the zeroed region shouldn't be deallocated.I think it would make sense to either update
write_zeroes()with FALLOC_FL_ZERO_RANGE or add an extra parameter to that function (modefor example) which can be anyFallocateModevariant.Moreover, we can completely switch to the latest crosvm
write_zeroeswhich is using FALLOC_FL_ZERO_RANGE forFileand adds a new traitWriteZeroesAtwhich lets you give the offset in file instead of using the current cursor. It also allows doing custom implementations for write_zeroes() (which might be useful for example for qcow file wrappers, example here).Any thoughts / suggestions?
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