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lxd/storage: Fix check for direct I/O write support #14157

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Sep 26, 2024
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lxd/storage: Fix check for direct I/O write support #14157

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2 changes: 1 addition & 1 deletion lxd/storage/backend_lxd.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1858,7 +1858,7 @@ func (b *lxdBackend) imageConversionFiller(imgPath string, imgFormat string, op
_ = from.Close()
}

to, err := os.OpenFile(diskPath, unix.O_DIRECT|unix.O_RDONLY, 0)
to, err := os.OpenFile(diskPath, unix.O_DIRECT|unix.O_WRONLY, 0)
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do we need this, we use O_RDONLY in ImageUnpack.

The aim is just to figure out if the underlying storage supports direct I/O, not to actually use the file handle.

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That's a good question I don't know the answer for. Can direct I/O support be different for writing and reading?

If not, then why check both from and to?

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NVM re from and to, they can be on different FS :)

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@mihalicyn do you know if O_DIRECT support can vary between read and write accesses? I'm well outside of my depth here but after reading the commit description of https://github.com/openzfs/zfs/pull/10018/commits, I believe it would be prudent to test for both type of operations.

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Hi Simon,

do you know if O_DIRECT support can vary between read and write accesses?

from what I see all r/w filesystems which support O_DIRECT support both modes. At the same time, in theory, filesystem may reject O_DIRECT writes and support read. But I wasn't able to find any existing filesystem with such a behavior.

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OK thanks

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Should this be similarly adjusted on ImageUnpack?

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yeah if its appropriate

if err == nil {
cmd = append(cmd, "-t", "none")
_ = to.Close()
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