Re: [libvirt] [PATCHv2 02/11] storage: Fix implementation of no-overwrite for file system backend

https://bugzilla.redhat.com/show_bug.cgi?id=1363586 Commit id '27758859' introduced the "NO_OVERWRITE" flag check for file system backends; however, the implementation, documentation, and algorithm was inconsistent. For the "flag" description for the API the flag was described as "Do not overwrite existing pool"; however, within the storage backend code the flag is described as "it probes to determine if filesystem already exists on the target device, renurning an error if exists". The code itself was implemented using the paradigm to set up the superblock probe by creating a filter that would cause the code to only search for the provided format type. If that type wasn't found, then the algorithm would return success allowing the caller to format the device. If the format type already existed on the device, then the code would fail indicating that the a filesystem of the same type existed on the device. The result is that if someone had a file system of one type on the device, it was possible to overwrite it if a different format type was specified in updated XML effectively trashing whatever was on the device already. This patch alters what NO_OVERWRITE does for a file system backend to be more realistic and consistent with what should be expected when the caller requests to not overwrite the data on the disk. Rather than filter results based on the expected format type, the code will allow success/failure be determined solely on whether the blkid_do_probe calls finds some known format on the device. This adjustment also allows removal of the virStoragePoolProbeResult enum that was under utilized. If it does find a formatted file system different errors will be generated indicating a file system of a specific type already exists or a file system of some other type already exists. In the original virsh support commit id 'ddcd5674', the description for '--no-overwrite' within the 'pool-build' command help output has an ambiguous "of this type" included in the short description. Compared to the longer description within the "Build a given pool." section of the virsh.pod file it's more apparent that the meaning of this flag would cause failure if a probe of the target already has a filesystem. So this patch also modifies the short description to just be the antecedent of the 'overwrite' flag, which matches the API description. This patch also modifies the grammar in virsh.pod for no-overwrite as well as reworking the paragraph formats to make it easier to read. Signed-off-by: John Ferlan <jferlan(a)redhat.com&gt; --- v1: http://www.redhat.com/archives/libvir-list/2016-November/msg00784.html Changes aplenty since v1 - the subsequent patches are a result of the review comments from jtomko vis-a-vis using blkid for the partitions src/storage/storage_backend.c | 68 ++++++++++++++++++---------------------- src/storage/storage_backend_fs.c | 15 +++++---- src/storage/storage_backend_fs.h | 5 --- tools/virsh-pool.c | 2 +- tools/virsh.pod | 32 ++++++++++--------- 5 files changed, 58 insertions(+), 64 deletions(-) diff --git a/src/storage/storage_backend.c b/src/storage/storage_backend.c index 2432b54..108f2b9 100644 --- a/src/storage/storage_backend.c +++ b/src/storage/storage_backend.c @@ -2646,87 +2646,80 @@ virStorageBackendFindGlusterPoolSources(const char *host ATTRIBUTE_UNUSED, * Use the blkid_ APIs in order to get details regarding whether a file * system exists on the disk already. * - * Returns @virStoragePoolProbeResult value, where any error will also - * set the error message. + * Returns: + * -1: An error was encountered, with error message set + * 0: No file system found

*/ -static virStoragePoolProbeResult +static int virStorageBackendBLKIDProbeFS(const char *device, const char *format) { - virStoragePoolProbeResult ret = FILESYSTEM_PROBE_ERROR; + int ret = -1; blkid_probe probe = NULL; const char *fstype = NULL; - char *names[2], *libblkid_format = NULL; VIR_DEBUG("Probing for existing filesystem of type %s on device %s", format, device); if (blkid_known_fstype(format) == 0) { virReportError(VIR_ERR_STORAGE_PROBE_FAILED, - _("Not capable of probing for " - "filesystem of type %s"), + _("Not capable of probing for filesystem of " + "type %s, requires --overwrite"), format); - goto error; + return -1; } - probe = blkid_new_probe_from_filename(device); - if (probe == NULL) { + if (!(probe = blkid_new_probe_from_filename(device))) { virReportError(VIR_ERR_STORAGE_PROBE_FAILED, - _("Failed to create filesystem probe " - "for device %s"), + _("Failed to create filesystem probe for device %s"), device); - goto error; + return -1; } - if (VIR_STRDUP(libblkid_format, format) < 0) - goto error; - - names[0] = libblkid_format; - names[1] = NULL; - - blkid_probe_filter_superblocks_type(probe, - BLKID_FLTR_ONLYIN, - names); - if (blkid_do_probe(probe) != 0) { VIR_INFO("No filesystem of type '%s' found on device '%s'", format, device); - ret = FILESYSTEM_PROBE_NOT_FOUND; } else if (blkid_probe_lookup_value(probe, "TYPE", &fstype, NULL) == 0) { - virReportError(VIR_ERR_STORAGE_POOL_BUILT, - _("Existing filesystem of type '%s' found on " - "device '%s'"), - fstype, device); - ret = FILESYSTEM_PROBE_FOUND; + if (STREQ(fstype, format)) { + virReportError(VIR_ERR_STORAGE_POOL_BUILT, + _("Device '%s' already contains a filesystem " + "of type '%s'"), + device, fstype); + } else { + virReportError(VIR_ERR_STORAGE_POOL_BUILT, + _("Existing filesystem of type '%s' found on " + "device '%s', requires --overwrite"), + fstype, device); + } + goto cleanup; } if (blkid_do_probe(probe) != 1) { virReportError(VIR_ERR_STORAGE_PROBE_FAILED, "%s", _("Found additional probes to run, " "filesystem probing may be incorrect")); - ret = FILESYSTEM_PROBE_ERROR; + goto cleanup; } - error: - VIR_FREE(libblkid_format); + ret = 0; - if (probe != NULL) - blkid_free_probe(probe); + cleanup: + blkid_free_probe(probe); return ret; }