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>
0485e53675