db2bc43017
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>
52 lines
1.5 KiB
Go
52 lines
1.5 KiB
Go
// +build linux
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package loopback // import "github.com/docker/docker/pkg/loopback"
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import (
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"unsafe"
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"golang.org/x/sys/unix"
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)
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func ioctlLoopCtlGetFree(fd uintptr) (int, error) {
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// The ioctl interface for /dev/loop-control (since Linux 3.1) is a bit
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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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}
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return int(ioctlReturn), nil
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}
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func ioctlLoopSetFd(loopFd, sparseFd uintptr) error {
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return unix.IoctlSetInt(int(loopFd), unix.LOOP_SET_FD, int(sparseFd))
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}
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func ioctlLoopSetStatus64(loopFd uintptr, loopInfo *unix.LoopInfo64) error {
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if _, _, err := unix.Syscall(unix.SYS_IOCTL, loopFd, unix.LOOP_SET_STATUS64, uintptr(unsafe.Pointer(loopInfo))); err != 0 {
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return err
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}
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return nil
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}
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func ioctlLoopClrFd(loopFd uintptr) error {
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if _, _, err := unix.Syscall(unix.SYS_IOCTL, loopFd, unix.LOOP_CLR_FD, 0); err != 0 {
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return err
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}
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return nil
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}
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func ioctlLoopGetStatus64(loopFd uintptr) (*unix.LoopInfo64, error) {
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loopInfo := &unix.LoopInfo64{}
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if _, _, err := unix.Syscall(unix.SYS_IOCTL, loopFd, unix.LOOP_GET_STATUS64, uintptr(unsafe.Pointer(loopInfo))); err != 0 {
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return nil, err
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}
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return loopInfo, nil
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}
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func ioctlLoopSetCapacity(loopFd uintptr, value int) error {
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return unix.IoctlSetInt(int(loopFd), unix.LOOP_SET_CAPACITY, value)
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}
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