Use correct `LOOP_CTL_GET_FREE` API in `pkg/loopback`
The `ioctl` interface for the `LOOP_CTL_GET_FREE` request on
`/dev/loop-control` is a little different from what `unix.IoctlGetInt`
expects: the first index is the returned status in `r1`, not an `int`
pointer as the first parameter.
Unfortunately we have to go a little lower level to get the appropriate
loop device index out, using `unix.Syscall` directly to read from
`r1`. Internally, the index is returned as a signed integer to match the
internal `ioctl` expectations of interpreting a negative signed integer
as an error at the userspace ABI boundary, so the direct interface of
`ioctlLoopCtlGetFree` can remain as-is.
[@kolyshkin: it still worked before this fix because of
/dev scan fallback in ioctlLoopCtlGetFree()]
Signed-off-by: Daniel Sweet <danieljsweet@icloud.com>
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
(cherry picked from commit db2bc43017
)
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
This commit is contained in:
parent
ed20165a37
commit
0485e53675
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@ -9,11 +9,15 @@ import (
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)
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)
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func ioctlLoopCtlGetFree(fd uintptr) (int, error) {
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func ioctlLoopCtlGetFree(fd uintptr) (int, error) {
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index, err := unix.IoctlGetInt(int(fd), LoopCtlGetFree)
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// The ioctl interface for /dev/loop-control (since Linux 3.1) is a bit
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if err != nil {
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// off compared to what you'd expect: instead of writing an integer to a
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// parameter pointer like unix.IoctlGetInt() expects, it returns the first
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// available loop device index directly.
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ioctlReturn, _, err := unix.Syscall(unix.SYS_IOCTL, fd, LoopCtlGetFree, 0)
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if err != 0 {
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return 0, err
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return 0, err
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}
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}
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return index, nil
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return int(ioctlReturn), nil
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}
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}
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func ioctlLoopSetFd(loopFd, sparseFd uintptr) error {
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func ioctlLoopSetFd(loopFd, sparseFd uintptr) error {
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