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Re: [libvirt] [PATCH 4/1] qemu: detect incomplete save files



On Tue, Aug 30, 2011 at 03:06:36PM -0600, Eric Blake wrote:
> Several users have reported problems with 'virsh start' failing because
> it was encountering a managed save situation where the managed save file
> was incomplete.  Be more robust to this by using two different magic
> numbers, so that newer libvirt can gracefully handle an incomplete file
> differently than a complete one, while older libvirt will at least fail
> up front rather than trying to load only to have qemu fail at the end.
> 
> Managed save is a convenience - it exists to preserve as much state
> as possible; if the state was not preserved, it is reasonable to just
> log that fact, then proceed with a fresh boot.  On the other hand,
> user saves are under user control, so we must fail, but by making
> the failure message distinct, the user can better decide how to handle
> the situation of an incomplete save file.
> 
> * src/qemu/qemu_driver.c (QEMUD_SAVE_PARTIAL): New define.
> (qemuDomainSaveInternal): Use it to mark incomplete images.
> (qemuDomainSaveImageOpen, qemuDomainObjRestore): Add parameter
> that controls what to do with partial images.
> (qemuDomainRestoreFlags, qemuDomainSaveImageGetXMLDesc)
> (qemuDomainSaveImageDefineXML, qemuDomainObjStart): Update callers.
> Based on an initial idea by Osier Yang.
> ---
> 
> This should implement everything mentioned here:
> https://www.redhat.com/archives/libvir-list/2011-August/msg00854.html
> 
>  src/qemu/qemu_driver.c |   84 ++++++++++++++++++++++++++++++++++++++----------
>  1 files changed, 67 insertions(+), 17 deletions(-)
> 
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 9cb034b..61b33fe 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -2111,9 +2111,12 @@ cleanup:
>  }
> 
> 
> -#define QEMUD_SAVE_MAGIC "LibvirtQemudSave"
> +#define QEMUD_SAVE_MAGIC   "LibvirtQemudSave"
> +#define QEMUD_SAVE_PARTIAL "LibvirtQemudPart"
>  #define QEMUD_SAVE_VERSION 2
> 
> +verify(sizeof(QEMUD_SAVE_MAGIC) == sizeof(QEMUD_SAVE_PARTIAL));
> +
>  enum qemud_save_formats {
>      QEMUD_SAVE_FORMAT_RAW = 0,
>      QEMUD_SAVE_FORMAT_GZIP = 1,
> @@ -2331,7 +2334,7 @@ qemuDomainSaveInternal(struct qemud_driver *driver, virDomainPtr dom,
>      }
> 
>      memset(&header, 0, sizeof(header));
> -    memcpy(header.magic, QEMUD_SAVE_MAGIC, sizeof(header.magic));
> +    memcpy(header.magic, QEMUD_SAVE_PARTIAL, sizeof(header.magic));
>      header.version = QEMUD_SAVE_VERSION;
> 
>      header.compressed = compressed;
> @@ -2435,12 +2438,37 @@ qemuDomainSaveInternal(struct qemud_driver *driver, virDomainPtr dom,
>                              bypassSecurityDriver,
>                              QEMU_ASYNC_JOB_SAVE) < 0)
>          goto endjob;
> +
> +    /* Touch up file header to mark image complete.  */
> +    if (bypass_cache) {
> +        /* Reopen the file to touch up the header, since we aren't set
> +         * up to seek backwards on directFd.  The reopened fd will
> +         * trigger a single page of file system cache pollution, but
> +         * that's acceptable.  */
> +        if (VIR_CLOSE(fd) < 0) {
> +            virReportSystemError(errno, _("unable to close %s"), path);
> +            goto endjob;
> +        }
> +        if (virFileDirectFdClose(directFd) < 0)
> +            goto endjob;
> +        fd = qemuOpenFile(driver, path, O_WRONLY, NULL, NULL);
> +        if (fd < 0)
> +            goto endjob;
> +    } else {
> +        if (lseek(fd, 0, SEEK_SET) != 0) {
> +            virReportSystemError(errno, _("unable to seek %s"), path);
> +            goto endjob;
> +        }
> +    }
> +    memcpy(header.magic, QEMUD_SAVE_MAGIC, sizeof(header.magic));
> +    if (safewrite(fd, &header, sizeof(header)) != sizeof(header)) {
> +        virReportSystemError(errno, _("unable to write %s"), path);
> +        goto endjob;
> +    }
>      if (VIR_CLOSE(fd) < 0) {
>          virReportSystemError(errno, _("unable to close %s"), path);
>          goto endjob;
>      }
> -    if (virFileDirectFdClose(directFd) < 0)
> -        goto endjob;
> 
>      ret = 0;
> 
> @@ -3769,15 +3797,16 @@ cleanup:
>      return ret;
>  }
> 
> -/* Return -1 on failure, -2 if edit was specified but xmlin does not
> - * represent any changes, and opened fd on all other success.  */
> +/* Return -1 on most failures after raising error, -2 if edit was specified
> + * but xmlin does not represent any changes (no error raised), -3 if corrupt
> + * image was unlinked (no error raised), and opened fd on success.  */
>  static int ATTRIBUTE_NONNULL(3) ATTRIBUTE_NONNULL(4)
>  qemuDomainSaveImageOpen(struct qemud_driver *driver,
>                          const char *path,
>                          virDomainDefPtr *ret_def,
>                          struct qemud_save_header *ret_header,
>                          bool bypass_cache, virFileDirectFdPtr *directFd,
> -                        const char *xmlin, bool edit)
> +                        const char *xmlin, bool edit, bool unlink_corrupt)
>  {
>      int fd;
>      struct qemud_save_header header;
> @@ -3807,8 +3836,22 @@ qemuDomainSaveImageOpen(struct qemud_driver *driver,
>      }
> 
>      if (memcmp(header.magic, QEMUD_SAVE_MAGIC, sizeof(header.magic)) != 0) {
> -        qemuReportError(VIR_ERR_OPERATION_FAILED,
> -                        "%s", _("image magic is incorrect"));
> +        const char *msg = _("image magic is incorrect");
> +
> +        if (memcmp(header.magic, QEMUD_SAVE_PARTIAL,
> +                   sizeof(header.magic)) == 0) {
> +            msg = _("save image is incomplete");
> +            if (unlink_corrupt) {
> +                if (VIR_CLOSE(fd) < 0 || unlink(path) < 0) {
> +                    virReportSystemError(errno,
> +                                         _("cannot remove corrupt file: %s"),
> +                                         path);
> +                    goto error;
> +                }
> +                return -3;
> +            }
> +        }
> +        qemuReportError(VIR_ERR_OPERATION_FAILED, "%s", msg);
>          goto error;
>      }
> 
> @@ -4009,7 +4052,7 @@ qemuDomainRestoreFlags(virConnectPtr conn,
> 
>      fd = qemuDomainSaveImageOpen(driver, path, &def, &header,
>                                   (flags & VIR_DOMAIN_SAVE_BYPASS_CACHE) != 0,
> -                                 &directFd, dxml, false);
> +                                 &directFd, dxml, false, false);
>      if (fd < 0)
>          goto cleanup;
> 
> @@ -4071,7 +4114,7 @@ qemuDomainSaveImageGetXMLDesc(virConnectPtr conn, const char *path,
>      qemuDriverLock(driver);
> 
>      fd = qemuDomainSaveImageOpen(driver, path, &def, &header, false, NULL,
> -                                 NULL, false);
> +                                 NULL, false, false);
> 
>      if (fd < 0)
>          goto cleanup;
> @@ -4102,7 +4145,7 @@ qemuDomainSaveImageDefineXML(virConnectPtr conn, const char *path,
>      qemuDriverLock(driver);
> 
>      fd = qemuDomainSaveImageOpen(driver, path, &def, &header, false, NULL,
> -                                 dxml, true);
> +                                 dxml, true, false);
> 
>      if (fd < 0) {
>          /* Check for special case of no change needed.  */
> @@ -4147,6 +4190,8 @@ cleanup:
>      return ret;
>  }
> 
> +/* Return 0 on success, 1 if incomplete saved image was silently unlinked,
> + * and -1 on failure with error raised.  */
>  static int
>  qemuDomainObjRestore(virConnectPtr conn,
>                       struct qemud_driver *driver,
> @@ -4161,9 +4206,12 @@ qemuDomainObjRestore(virConnectPtr conn,
>      virFileDirectFdPtr directFd = NULL;
> 
>      fd = qemuDomainSaveImageOpen(driver, path, &def, &header,
> -                                 bypass_cache, &directFd, NULL, false);
> -    if (fd < 0)
> +                                 bypass_cache, &directFd, NULL, false, true);
> +    if (fd < 0) {
> +        if (fd == -3)
> +            ret = 1;
>          goto cleanup;
> +    }
> 
>      if (STRNEQ(vm->def->name, def->name) ||
>          memcmp(vm->def->uuid, def->uuid, VIR_UUID_BUFLEN)) {
> @@ -4472,10 +4520,12 @@ qemuDomainObjStart(virConnectPtr conn,
>              ret = qemuDomainObjRestore(conn, driver, vm, managed_save,
>                                         bypass_cache);
> 
> -            if ((ret == 0) && (unlink(managed_save) < 0))
> +            if (ret == 0 && unlink(managed_save) < 0)
>                  VIR_WARN("Failed to remove the managed state %s", managed_save);
> -
> -            goto cleanup;
> +            if (ret > 0)
> +                VIR_WARN("Ignoring incomplete managed state %s", managed_save);
> +            else
> +                goto cleanup;
>          }
>      }

  Looks and sounds okay, ACK,

Daniel

-- 
Daniel Veillard      | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
daniel veillard com  | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library  http://libvirt.org/


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