On a Wednesday in 2020, Michal Privoznik wrote:
One of the symptoms of the bug [1] is that on the second start of a domain we get EBADF when talking to libdevmapper. The reason is that libdevmapper opens /dev/mapper/control to talk to kernel and saves the FD into a global variable. This works well when starting a domain for the first time: the pre-exec hook (which is a separate process) gets info it needs; then the daemon sets up CGroups (where it will open the file again, because it's a different process). Now, libdevmapper won't close this FD until library is unloaded (in destructor) or dm_lib_release() is called. We were not doing any of that, hence, when starting a domain (any domain, even a different one), we forked off a child process (which will eventually become QEMU), mass close all FDs (including the libdevmapper's one), and run pre-exec hook. Since we closed the FD, libdevmapper will pass closed FD into an ioctl() and thus we got EBADF. After previous patch, this approach is history and thus we should not see EBADF anymore. 1: https://bugzilla.redhat.com/show_bug.cgi?id=1858260
That bug is private.
Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
---
src/qemu/qemu_cgroup.c | 2 +-
src/qemu/qemu_domain.c | 4 ++--
src/util/virdevmapper.c | 3 ---
3 files changed, 3 insertions(+), 6 deletions(-)
diff --git a/src/qemu/qemu_cgroup.c b/src/qemu/qemu_cgroup.c
index 914bf640ca..e88da02341 100644
--- a/src/qemu/qemu_cgroup.c
+++ b/src/qemu/qemu_cgroup.c
@@ -87,7 +87,7 @@ qemuSetupImagePathCgroup(virDomainObjPtr vm,
}
if (virDevMapperGetTargets(path, &targetPaths) < 0 &&
- errno != ENOSYS && errno != EBADF) {
+ errno != ENOSYS) {
virReportSystemError(errno,
_("Unable to get devmapper targets for %s"),
path);
diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index 5b22eb2eaa..2058290870 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -10264,7 +10264,7 @@ qemuDomainSetupDisk(virQEMUDriverConfigPtr cfg G_GNUC_UNUSED,
return -1;
if (virDevMapperGetTargets(next->path, &targetPaths) < 0 &&
- errno != ENOSYS && errno != EBADF) {
+ errno != ENOSYS) {
virReportSystemError(errno,
_("Unable to get devmapper targets for %s"),
next->path);
@@ -11328,7 +11328,7 @@ qemuDomainNamespaceSetupDisk(virDomainObjPtr vm,
tmpPath = g_strdup(next->path);
if (virDevMapperGetTargets(next->path, &targetPaths) < 0 &&
- errno != ENOSYS && errno != EBADF) {
+ errno != ENOSYS) {
virReportSystemError(errno,
_("Unable to get devmapper targets for %s"),
next->path);
This changes the functions that are moved in the very next patch. Doing changes after the movement makes 'git blame' easier to use. Jano
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