[libvirt] [PATCHv3 12/16] blockjob: allow for existing files

[Eric Blake]

This copies some of the checks from snapshots regarding testing
when a file already exists.  In the process, I noticed a missing
sanity check in snapshots: REUSE_EXT should require the destination
to already be present.

* src/qemu/qemu_driver.c (qemuDomainBlockRebase): Allow REUSE_EXT
flag.
(qemuDomainBlockCopy): Wire up flag, and add some sanity checks.
(qemuDomainSnapshotDiskPrepare): Require destination on REUSE_EXT.
---
 src/qemu/qemu_driver.c |   61 +++++++++++++++++++++++++++++++++++++++++++----
 1 files changed, 55 insertions(+), 6 deletions(-)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 1b1c921..0e9ea41 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -9812,6 +9812,11 @@ qemuDomainSnapshotDiskPrepare(virDomainObjPtr vm, virDomainSnapshotDefPtr def,
                                          _("unable to stat for disk %s: %s"),
                                          disk->name, disk->file);
                     goto cleanup;
+                } else if (allow_reuse) {
+                    virReportSystemError(errno,
+                                         _("missing existing file for disk %s: %s"),
+                                         disk->name, disk->file);
+                    goto cleanup;
                 }
             } else if (!(S_ISBLK(st.st_mode) || !st.st_size || allow_reuse)) {
                 qemuReportError(VIR_ERR_CONFIG_UNSUPPORTED,
@@ -11881,9 +11886,11 @@ qemuDomainBlockCopy(virDomainPtr dom, const char *path,
     int ret = -1;
     int idx;
     int mode;
+    struct stat st;

     /* Preliminaries: find the disk we are editing, sanity checks */
-    virCheckFlags(VIR_DOMAIN_BLOCK_REBASE_SHALLOW, -1);
+    virCheckFlags(VIR_DOMAIN_BLOCK_REBASE_SHALLOW |
+                  VIR_DOMAIN_BLOCK_REBASE_REUSE_EXT, -1);

     qemuDriverLock(driver);
     virUUIDFormat(dom->uuid, uuidstr);
@@ -11928,19 +11935,60 @@ qemuDomainBlockCopy(virDomainPtr dom, const char *path,
         goto endjob;
     }

+    if ((flags & VIR_DOMAIN_BLOCK_REBASE_SHALLOW) &&
+        STREQ_NULLABLE(format, "raw") &&
+        STRNEQ_NULLABLE(disk->driverType, "raw")) {
+        qemuReportError(VIR_ERR_INVALID_ARG,
+                        _("raw shallow copy of non-raw disk '%s' not possible"),
+                        disk->dst);
+        goto endjob;
+    }
+    /* XXX this is pessimistic; we could use 'query-block' or even
+     * keep track of the backing chain ourselves, rather than assuming
+     * that all non-raw source files have a current backing image */
+    if ((flags & VIR_DOMAIN_BLOCK_REBASE_REUSE_EXT) &&
+        !(flags & VIR_DOMAIN_BLOCK_REBASE_SHALLOW) &&
+        STRNEQ_NULLABLE(disk->driverType, "raw")) {
+        qemuReportError(VIR_ERR_ARGUMENT_UNSUPPORTED,
+                        _("non-shallow copy of non-raw disk '%s' to existing "
+                          "destination not supported"),
+                        disk->dst);
+        goto endjob;
+    }
+
     /* Prepare the destination file.  */
+    if (stat(dest, &st) < 0) {
+        if (errno != ENOENT) {
+            virReportSystemError(errno, _("unable to stat for disk %s: %s"),
+                                 disk->dst, dest);
+            goto endjob;
+        } else if (flags & VIR_DOMAIN_BLOCK_REBASE_REUSE_EXT) {
+            virReportSystemError(errno,
+                                 _("missing destination file for disk %s: %s"),
+                                 disk->dst, dest);
+            goto endjob;
+        }
+    } else if (!(S_ISBLK(st.st_mode) || !st.st_size ||
+                 (flags & VIR_DOMAIN_BLOCK_REBASE_REUSE_EXT))) {
+        qemuReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                        _("external destination file for disk %s already "
+                          "exists and is not a block device: %s"),
+                        disk->dst, dest);
+        goto endjob;
+    }
+
     /* XXX We also need to add security labeling, lock manager lease,
-     * and auditing of those events, as well as to support reuse of
-     * existing images, including probing the existing format of an
-     * existing image.  */
-    if (!format)
+     * and auditing of those events.  */
+    if (!format && !(flags & VIR_DOMAIN_BLOCK_REBASE_REUSE_EXT))
         format = disk->driverType;
     if ((format && !(disk->mirrorFormat = strdup(format))) ||
         !(disk->mirror = strdup(dest))) {
         virReportOOMError();
         goto endjob;
     }
-    if (flags & VIR_DOMAIN_BLOCK_REBASE_SHALLOW)
+    if (flags & VIR_DOMAIN_BLOCK_REBASE_REUSE_EXT)
+        mode = QEMU_MONITOR_DRIVE_MIRROR_EXISTING;
+    else if (flags & VIR_DOMAIN_BLOCK_REBASE_SHALLOW)
         mode = QEMU_MONITOR_DRIVE_MIRROR_ABSOLUTE;
     else
         mode = QEMU_MONITOR_DRIVE_MIRROR_NO_BACKING;
@@ -11976,6 +12024,7 @@ qemuDomainBlockRebase(virDomainPtr dom, const char *path, const char *base,
                       unsigned long bandwidth, unsigned int flags)
 {
     virCheckFlags(VIR_DOMAIN_BLOCK_REBASE_SHALLOW |
+                  VIR_DOMAIN_BLOCK_REBASE_REUSE_EXT |
                   VIR_DOMAIN_BLOCK_REBASE_COPY |
                   VIR_DOMAIN_BLOCK_REBASE_COPY_RAW, -1);

-- 
1.7.7.6