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/openbmc/qemu/tests/qemu-iotests/tests/ |
H A D | write-zeroes-unmap.out | d05ae948 Fri Jun 28 15:20:58 CDT 2024 Nir Soffer <nsoffer@redhat.com> Consider discard option when writing zeros
When opening an image with discard=off, we punch hole in the image when writing zeroes, making the image sparse. This breaks users that want to ensure that writes cannot fail with ENOSPACE by using fully allocated images[1].
bdrv_co_pwrite_zeroes() correctly disables BDRV_REQ_MAY_UNMAP if we opened the child without discard=unmap or discard=on. But we don't go through this function when accessing the top node. Move the check down to bdrv_co_do_pwrite_zeroes() which seems to be used in all code paths.
This change implements the documented behavior, punching holes only when opening the image with discard=on or discard=unmap. This may not be the best default but can improve it later.
The test depends on a file system supporting discard, deallocating the entire file when punching hole with the length of the entire file. Tested with xfs, ext4, and tmpfs.
[1] https://lists.nongnu.org/archive/html/qemu-discuss/2024-06/msg00003.html
Signed-off-by: Nir Soffer <nsoffer@redhat.com> Message-id: 20240628202058.1964986-3-nsoffer@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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H A D | write-zeroes-unmap | d05ae948 Fri Jun 28 15:20:58 CDT 2024 Nir Soffer <nsoffer@redhat.com> Consider discard option when writing zeros
When opening an image with discard=off, we punch hole in the image when writing zeroes, making the image sparse. This breaks users that want to ensure that writes cannot fail with ENOSPACE by using fully allocated images[1].
bdrv_co_pwrite_zeroes() correctly disables BDRV_REQ_MAY_UNMAP if we opened the child without discard=unmap or discard=on. But we don't go through this function when accessing the top node. Move the check down to bdrv_co_do_pwrite_zeroes() which seems to be used in all code paths.
This change implements the documented behavior, punching holes only when opening the image with discard=on or discard=unmap. This may not be the best default but can improve it later.
The test depends on a file system supporting discard, deallocating the entire file when punching hole with the length of the entire file. Tested with xfs, ext4, and tmpfs.
[1] https://lists.nongnu.org/archive/html/qemu-discuss/2024-06/msg00003.html
Signed-off-by: Nir Soffer <nsoffer@redhat.com> Message-id: 20240628202058.1964986-3-nsoffer@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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/openbmc/qemu/block/ |
H A D | io.c | d05ae948 Fri Jun 28 15:20:58 CDT 2024 Nir Soffer <nsoffer@redhat.com> Consider discard option when writing zeros
When opening an image with discard=off, we punch hole in the image when writing zeroes, making the image sparse. This breaks users that want to ensure that writes cannot fail with ENOSPACE by using fully allocated images[1].
bdrv_co_pwrite_zeroes() correctly disables BDRV_REQ_MAY_UNMAP if we opened the child without discard=unmap or discard=on. But we don't go through this function when accessing the top node. Move the check down to bdrv_co_do_pwrite_zeroes() which seems to be used in all code paths.
This change implements the documented behavior, punching holes only when opening the image with discard=on or discard=unmap. This may not be the best default but can improve it later.
The test depends on a file system supporting discard, deallocating the entire file when punching hole with the length of the entire file. Tested with xfs, ext4, and tmpfs.
[1] https://lists.nongnu.org/archive/html/qemu-discuss/2024-06/msg00003.html
Signed-off-by: Nir Soffer <nsoffer@redhat.com> Message-id: 20240628202058.1964986-3-nsoffer@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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