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128 lines
4.2 KiB
Go
128 lines
4.2 KiB
Go
//go:build linux && cgo && !static_build && libdm_dlsym_deferred_remove && !libdm_no_deferred_remove
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// +build linux,cgo,!static_build,libdm_dlsym_deferred_remove,!libdm_no_deferred_remove
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package devicemapper
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/*
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#cgo LDFLAGS: -ldl
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#include <stdlib.h>
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#include <dlfcn.h>
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#include <libdevmapper.h>
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// Yes, I know this looks scary. In order to be able to fill our own internal
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// dm_info with deferred_remove we need to have a struct definition that is
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// correct (regardless of the version of libdm that was used to compile it). To
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// this end, we define struct_backport_dm_info. This code comes from lvm2, and
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// I have verified that the structure has only ever had elements *appended* to
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// it (since 2001).
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//
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// It is also important that this structure be _larger_ than the dm_info that
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// libdevmapper expected. Otherwise libdm might try to write to memory it
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// shouldn't (they don't have a "known size" API).
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struct backport_dm_info {
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int exists;
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int suspended;
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int live_table;
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int inactive_table;
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int32_t open_count;
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uint32_t event_nr;
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uint32_t major;
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uint32_t minor;
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int read_only;
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int32_t target_count;
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int deferred_remove;
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int internal_suspend;
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// Padding, purely for our own safety. This is to avoid cases where libdm
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// was updated underneath us and we call into dm_task_get_info() with too
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// small of a buffer.
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char _[512];
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};
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// We have to wrap this in CGo, because Go really doesn't like function pointers.
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int call_dm_task_deferred_remove(void *fn, struct dm_task *task)
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{
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int (*_dm_task_deferred_remove)(struct dm_task *task) = fn;
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return _dm_task_deferred_remove(task);
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}
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*/
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import "C"
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import (
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"unsafe"
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"github.com/sirupsen/logrus"
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)
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// dm_task_deferred_remove is not supported by all distributions, due to
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// out-dated versions of devicemapper. However, in the case where the
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// devicemapper library was updated without rebuilding Docker (which can happen
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// in some distributions) then we should attempt to dynamically load the
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// relevant object rather than try to link to it.
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// dmTaskDeferredRemoveFct is a "bound" version of dm_task_deferred_remove.
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// It is nil if dm_task_deferred_remove was not found in the libdevmapper that
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// is currently loaded.
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var dmTaskDeferredRemovePtr unsafe.Pointer
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// LibraryDeferredRemovalSupport tells if the feature is supported by the
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// current Docker invocation. This value is fixed during init.
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var LibraryDeferredRemovalSupport bool
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func init() {
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// Clear any errors.
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var err *C.char
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C.dlerror()
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// The symbol we want to fetch.
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symName := C.CString("dm_task_deferred_remove")
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defer C.free(unsafe.Pointer(symName))
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// See if we can find dm_task_deferred_remove. Since we already are linked
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// to libdevmapper, we can search our own address space (rather than trying
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// to guess what libdevmapper is called). We use NULL here, as RTLD_DEFAULT
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// is not available in CGO (even if you set _GNU_SOURCE for some reason).
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// The semantics are identical on glibc.
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sym := C.dlsym(nil, symName)
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err = C.dlerror()
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if err != nil {
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logrus.Debugf("devmapper: could not load dm_task_deferred_remove: %s", C.GoString(err))
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return
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}
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logrus.Debugf("devmapper: found dm_task_deferred_remove at %x", uintptr(sym))
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dmTaskDeferredRemovePtr = sym
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LibraryDeferredRemovalSupport = true
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}
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func dmTaskDeferredRemoveFct(task *cdmTask) int {
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sym := dmTaskDeferredRemovePtr
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if sym == nil || !LibraryDeferredRemovalSupport {
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return -1
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}
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return int(C.call_dm_task_deferred_remove(sym, (*C.struct_dm_task)(task)))
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}
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func dmTaskGetInfoWithDeferredFct(task *cdmTask, info *Info) int {
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if !LibraryDeferredRemovalSupport {
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return -1
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}
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Cinfo := C.struct_backport_dm_info{}
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defer func() {
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info.Exists = int(Cinfo.exists)
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info.Suspended = int(Cinfo.suspended)
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info.LiveTable = int(Cinfo.live_table)
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info.InactiveTable = int(Cinfo.inactive_table)
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info.OpenCount = int32(Cinfo.open_count)
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info.EventNr = uint32(Cinfo.event_nr)
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info.Major = uint32(Cinfo.major)
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info.Minor = uint32(Cinfo.minor)
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info.ReadOnly = int(Cinfo.read_only)
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info.TargetCount = int32(Cinfo.target_count)
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info.DeferredRemove = int(Cinfo.deferred_remove)
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}()
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return int(C.dm_task_get_info((*C.struct_dm_task)(task), (*C.struct_dm_info)(unsafe.Pointer(&Cinfo))))
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}
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