Add a qcow2-to-stdout Python script
#6559
Merged
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Taken from https://github.com/qemu/qemu/blob/a9cd5bc6399a80fcf233ed0fffe6067b731227d8/scripts/qcow2-to-stdout.py > This tool converts a disk image to qcow2, writing the result directly > to stdout. This can be used for example to send the generated file > over the network. > > This is equivalent to using qemu-img to convert a file to qcow2 and > then writing the result to stdout, with the difference that this tool > does not need to create this temporary qcow2 file and therefore does > not need any additional disk space. Signed-off-by: Andrii Sultanov <[email protected]>
We are only ever going to use this script with "raw" files. Signed-off-by: Andrii Sultanov <[email protected]>
The original script is designed to only work on regular files. Adapt it slightly to work on special block devices (since that's what we want to export from). Aside from dropping some unnecessary checks and replacing os.path.getsize with a functional equivalent that works on block special files, these changes remove detection of "holes" in the raw file, since SEEK_DATA and SEEK_HOLE are unimplemented in this case. Signed-off-by: Andrii Sultanov <[email protected]>
…sters When specified, only the clusters that have changed between diff_file_name and input_file will be allocated and exported in a sparse manner. This is analogous to vhd-tool's --relative-to option. Example usage: ``` Create an empty raw file: $ dd if=/dev/zero of=disk.before.img bs=1M count=100 Fill the first three clusters with random data $ dd if=/dev/random conv=notrunc of=disk.before.img bs=65536 count=3 $ python3/libexec/qcow2-to-stdout.py disk.before.img > disk.before.qcow2 Check that only the first three clusters are allocated (each is 0x10000 in length) $ qemu-img map disk.before.qcow2 Offset Length Mapped to File 0 0x30000 0x50000 disk.before.qcow2 Overwrite the 2nd and 3rd clusters with new data $ cp disk.before.img disk.after.img $ dd if=/dev/random conv=notrunc of=disk.after.img bs=65536 count=2 oseek=1 Export the difference, verifying that only the 2nd and 3rd clusters are allocated $ python3/libexec/qcow2-to-stdout.py disk.after.img --diff disk.before.img > disk.diff.qcow2 $ qemu-img map disk.diff.qcow2 Offset Length Mapped to File 0x10000 0x20000 0x50000 disk.diff.qcow2 The image can be recreated if the base is imported first, with the difference overwriting it $ qemu-img convert -f qcow2 -O raw disk.before.qcow2 disk.test.img $ qemu-img convert -f qcow2 -O raw disk.diff.qcow2 disk.test.img --target-is-zero -n $ diff disk.test.img disk.after.img <the same> ``` Signed-off-by: Andrii Sultanov <[email protected]>
|
This script also needs to be added to the specfile (if only we had an upstream one 🤔) : /opt/xensource/libexec/usb_scan.py
+/opt/xensource/libexec/qcow2-to-stdout.py
/etc/xensource/usb-policy.conf |
|
hopefully the dog with the warnings apepars only during reviews and doesn't block anything. I've yet to review the diff feature |
psafont
approved these changes
Jun 30, 2025
lindig
approved these changes
Jul 4, 2025
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
This script serves as one half of a
vhd-tool-like solution for QCOW, only offering the export side (converting a raw file to a qcow2 stream). We can't useqemu-imgor some other ready-made library because these create a temporary file (seeking in both the source and the destination), which we want to avoid.The script is taken from upstream QEMU, with some modifications for our use-case:
vhd-tooldoesThe script is currently unused.
The import half (
qcow2 stream->raw file) was merged inocaml-qcowand will later be integrated into xapi together with this script through aqcow_tool_wrapper.