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snapshot: refuse to generate names for non-regular backing files

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For whatever reason, the kernel allows you to create a regular
file named /dev/sdc.12345; although this file will disappear the
next time devtmpfs is remounted.  If you let libvirt generate
the name of the external snapshot for a disk image originally
using the block device /dev/sdc, then the domain will be rendered
unbootable once the qcow2 file is lost on the next devtmpfs
remount.  In this case, the user should have used 'virsh
snapshot-create --xmlfile' or 'virsh snapshot-create-as --diskspec'
to specify the name for the qcow2 file in a sane location, rather
than relying on libvirt generating a name that is most likely to
be wrong.  We can help avoid naive mistakes by enforcing that
the user provide the external name for any backing file that is
not a regular file.

* src/conf/domain_conf.c (virDomainSnapshotAlignDisks): Only
generate names if backing file exists as regular file.
Reported by MATSUDA Daiki.
This commit is contained in:
Eric Blake 2011-11-15 17:19:20 -07:00
parent d47ab3fe61
commit c74b97156f
1 changed files with 13 additions and 2 deletions
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15
src/conf/domain_conf.c
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@ -12203,7 +12203,8 @@ virDomainSnapshotAlignDisks(virDomainSnapshotDefPtr def,
qsort(&def->disks[0], def->ndisks, sizeof(def->disks[0]), disksorter); qsort(&def->disks[0], def->ndisks, sizeof(def->disks[0]), disksorter);
/* Generate any default external file names. */ /* Generate any default external file names, but only if the
* backing file is a regular file. */
for (i = 0; i < def->ndisks; i++) { for (i = 0; i < def->ndisks; i++) {
virDomainSnapshotDiskDefPtr disk = &def->disks[i]; virDomainSnapshotDiskDefPtr disk = &def->disks[i];
@ -12211,14 +12212,24 @@ virDomainSnapshotAlignDisks(virDomainSnapshotDefPtr def,
!disk->file) { !disk->file) {
const char *original = def->dom->disks[i]->src; const char *original = def->dom->disks[i]->src;
const char *tmp; const char *tmp;
struct stat sb;
if (!original) { if (!original) {
virDomainReportError(VIR_ERR_CONFIG_UNSUPPORTED, virDomainReportError(VIR_ERR_CONFIG_UNSUPPORTED,
_("cannot generate external backup name " _("cannot generate external snapshot name "
"for disk '%s' without source"), "for disk '%s' without source"),
disk->name); disk->name);
goto cleanup; goto cleanup;
} }
if (stat(original, &sb) < 0 || !S_ISREG(sb.st_mode)) {
virDomainReportError(VIR_ERR_CONFIG_UNSUPPORTED,
_("source for disk '%s' is not a regular "
"file; refusing to generate external "
"snapshot name"),
disk->name);
goto cleanup;
}
tmp = strrchr(original, '.'); tmp = strrchr(original, '.');
if (!tmp || strchr(tmp, '/')) { if (!tmp || strchr(tmp, '/')) {
ignore_value(virAsprintf(&disk->file, "%s.%s", ignore_value(virAsprintf(&disk->file, "%s.%s",