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[19.03 backport] Use correct LOOP_CTL_GET_FREE API in pkg/loopback#347
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thaJeztah merged 1 commit intodocker-archive:19.03from Sep 6, 2019
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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 db2bc43) Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
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Backport of PR moby#39801
The
ioctlinterface for theLOOP_CTL_GET_FREErequest on/dev/loop-controlis a little different from whatunix.IoctlGetIntexpects: the first index is the returned status in
r1, not anintpointer as the first parameter.
Unfortunately we have to go a little lower level to get the appropriate
loop device index out, using
unix.Syscalldirectly to read fromr1. Internally, the index is returned as a signed integer to match theinternal
ioctlexpectations of interpreting a negative signed integeras an error at the userspace ABI boundary, so the direct interface of
ioctlLoopCtlGetFreecan remain as-is.[@kolyshkin: it still worked before this fix because of
/dev scan fallback in ioctlLoopCtlGetFree()]