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qemu_namespace: Be less aggressive in removing /dev nodes from namespace

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When creating /dev nodes in a QEMU domain's namespace the first
thing we simply do is unlink() the path and create it again. This
aims to solve the case when a file changed type/major/minor in
the host and thus we need to reflect this in the guest's
namespace. Fair enough, except we can be a bit more clever about
it: firstly check whether the path doesn't already exist or isn't
already of the correct type/major/minor and do the
unlink+creation only if needed.

Currently, this is implemented only for symlinks and
block/character devices. For regular files/directories (which are
less common) this might be implemented one day, but not today.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
This commit is contained in:
Michal Privoznik 2022-03-14 13:35:15 +01:00
parent 9d749998b3
commit 22188790ca
1 changed files with 44 additions and 27 deletions
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71
src/qemu/qemu_namespace.c
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@ -948,38 +948,55 @@ qemuNamespaceMknodOne(qemuNamespaceMknodItem *data)
}
if (isLink) {
VIR_DEBUG("Creating symlink %s -> %s", data->file, data->target);
g_autoptr(GError) gerr = NULL;
g_autofree char *target = NULL;
/* First, unlink the symlink target. Symlinks change and
* therefore we have no guarantees that pre-existing
* symlink is still valid. */
if (unlink(data->file) < 0 &&
errno != ENOENT) {
virReportSystemError(errno,
_("Unable to remove symlink %s"),
data->file);
goto cleanup;
}
if (symlink(data->target, data->file) < 0) {
virReportSystemError(errno,
_("Unable to create symlink %s (pointing to %s)"),
data->file, data->target);
goto cleanup;
if ((target = g_file_read_link(data->file, &gerr)) &&
STREQ(target, data->target)) {
VIR_DEBUG("Skipping symlink %s -> %s which exists and points to correct target",
data->file, data->target);
} else {
delDevice = true;
VIR_DEBUG("Creating symlink %s -> %s", data->file, data->target);
/* First, unlink the symlink target. Symlinks change and
* therefore we have no guarantees that pre-existing
* symlink is still valid. */
if (unlink(data->file) < 0 &&
errno != ENOENT) {
virReportSystemError(errno,
_("Unable to remove symlink %s"),
data->file);
goto cleanup;
}
if (symlink(data->target, data->file) < 0) {
virReportSystemError(errno,
_("Unable to create symlink %s (pointing to %s)"),
data->file, data->target);
goto cleanup;
} else {
delDevice = true;
}
}
} else if (isDev) {
VIR_DEBUG("Creating dev %s (%d,%d)",
data->file, major(data->sb.st_rdev), minor(data->sb.st_rdev));
unlink(data->file);
if (mknod(data->file, data->sb.st_mode, data->sb.st_rdev) < 0) {
virReportSystemError(errno,
_("Unable to create device %s"),
data->file);
goto cleanup;
GStatBuf sb;
if (g_lstat(data->file, &sb) >= 0 &&
sb.st_rdev == data->sb.st_rdev) {
VIR_DEBUG("Skipping dev %s (%d,%d) which exists and has correct MAJ:MIN",
data->file, major(data->sb.st_rdev), minor(data->sb.st_rdev));
} else {
delDevice = true;
VIR_DEBUG("Creating dev %s (%d,%d)",
data->file, major(data->sb.st_rdev), minor(data->sb.st_rdev));
unlink(data->file);
if (mknod(data->file, data->sb.st_mode, data->sb.st_rdev) < 0) {
virReportSystemError(errno,
_("Unable to create device %s"),
data->file);
goto cleanup;
} else {
delDevice = true;
}
}
} else if (isReg || isDir) {
/* We are not cleaning up disks on virDomainDetachDevice