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Re: [libvirt] [PATCH 1/3] blockjob: add virDomainBlockCommit



On 09/18/12 00:08, Eric Blake wrote:
This API matches a proposed qemu command 'block-commit':
https://lists.gnu.org/archive/html/qemu-devel/2012-09/msg02226.html

Jeff's command is still in the works for qemu 1.3, and may gain
further enhancements, such as the ability to control on-error
handling (it will be comparable to the error handling Paolo is
adding to 'drive-mirror', so a similar solution will be needed
when I finally propose virDomainBlockCopy).  However, even without
qemu support, this API will be useful for _offline_ block commits,
by wrapping qemu-img calls and turning them into a block job, so
this API is worth committing now.

For some examples of how this will be implemented, all starting
with the chain: base <- snap1 <- snap2 <- active

+ These are equivalent:
  virDomainBlockCommit(dom, disk, NULL, NULL, 0, 0)
  virDomainBlockCommit(dom, disk, NULL, "active", 0, 0)
  virDomainBlockCommit(dom, disk, "base", NULL, 0, 0)
  virDomainBlockCommit(dom, disk, "base", "active", 0, 0)
but cannot be implemented for online qemu with round 1 of
Jeff's patches; and for offline images, it would require
three back-to-back qemu-img invocations unless qemu-img
is patched to allow more efficient multi-layer commits;
the end result would be 'base' as the active disk with
contents from all three other files, where 'snap1' and
'snap2' are invalid right away, and 'active' is invalid
once any further changes to 'base' are made, for a final
chain of base.

+ These are equivalent:
  virDomainBlockCommit(dom, disk, "snap2", NULL, 0, 0)
  virDomainBlockCommit(dom, disk, NULL, NULL, 0, _SHALLOW)
they cannot be implemented for online qemu, but for offline,
it is a matter of 'qemu-img commit active', so that 'snap2'
is now the active disk with contents formerly in 'active',
for a final chain of base <- snap1 <- snap2.

+ Similarly:
  virDomainBlockCommit(dom, disk, "snap2", NULL, 0, _DELETE)
for an offline domain will merge 'active' into 'snap2', then
delete 'active' to avoid leaving a potentially invalid file
around.

+ This version:
  virDomainBlockCommit(dom, disk, NULL, "snap2", 0, _SHALLOW)
can be implemented online with 'block-commit' passing a base of
snap1 and a top of snap2; and can be implemented offline by
'qemu-img commit snap2' followed by 'qemu-img rebase -u
-b snap1 active', for a final chain of base <- snap1 <- active.

* include/libvirt/libvirt.h.in (virDomainBlockCommit): New API.
* src/libvirt.c (virDomainBlockCommit): Implement it.
* src/libvirt_public.syms (LIBVIRT_0.10.2): Export it.
* src/driver.h (virDrvDomainBlockCommit): New driver callback.
* docs/apibuild.py (CParser.parseSignature): Add exception.
---
  docs/apibuild.py             |   1 +
  include/libvirt/libvirt.h.in |  20 +++++++++
  src/driver.h                 |   5 +++
  src/libvirt.c                | 105 +++++++++++++++++++++++++++++++++++++++++++
  src/libvirt_public.syms      |   1 +
  5 files changed, 132 insertions(+)

diff --git a/docs/apibuild.py b/docs/apibuild.py
index 3f0ecd9..ae84be9 100755
--- a/docs/apibuild.py
+++ b/docs/apibuild.py
@@ -1759,6 +1759,7 @@ class CParser:
          "virDomainSetMaxMemory"          : (False, ("memory")),
          "virDomainSetMemory"             : (False, ("memory")),
          "virDomainSetMemoryFlags"        : (False, ("memory")),
+        "virDomainBlockCommit"           : (False, ("bandwidth")),
          "virDomainBlockJobSetSpeed"      : (False, ("bandwidth")),
          "virDomainBlockPull"             : (False, ("bandwidth")),
          "virDomainBlockRebase"           : (False, ("bandwidth")),
diff --git a/include/libvirt/libvirt.h.in b/include/libvirt/libvirt.h.in
index 8f72c03..2fd8ae1 100644
--- a/include/libvirt/libvirt.h.in
+++ b/include/libvirt/libvirt.h.in
@@ -2062,11 +2062,14 @@ int virDomainUpdateDeviceFlags(virDomainPtr domain,
   * virDomainBlockRebase without flags), job ends on completion
   * VIR_DOMAIN_BLOCK_JOB_TYPE_COPY: Block Copy (virDomainBlockRebase with
   * flags), job exists as long as mirroring is active
+ * VIR_DOMAIN_BLOCK_JOB_TYPE_COMMIT: Block Commit (virDomainBlockCommit),
+ * job ends on completion
   */
  typedef enum {
      VIR_DOMAIN_BLOCK_JOB_TYPE_UNKNOWN = 0,
      VIR_DOMAIN_BLOCK_JOB_TYPE_PULL = 1,
      VIR_DOMAIN_BLOCK_JOB_TYPE_COPY = 2,
+    VIR_DOMAIN_BLOCK_JOB_TYPE_COMMIT = 3,

  #ifdef VIR_ENUM_SENTINELS
      VIR_DOMAIN_BLOCK_JOB_TYPE_LAST
@@ -2131,6 +2134,23 @@ int           virDomainBlockRebase(virDomainPtr dom, const char *disk,
                                     const char *base, unsigned long bandwidth,
                                     unsigned int flags);

+/**
+ * virDomainBlockCommitFlags:
+ *
+ * Flags available for virDomainBlockCommit().
+ */
+typedef enum {
+    VIR_DOMAIN_BLOCK_COMMIT_SHALLOW = 1 << 0, /* NULL base means next backing
+                                                 file, not whole chain */
+    VIR_DOMAIN_BLOCK_COMMIT_DELETE  = 1 << 1, /* Delete any files that are now
+                                                 invalid after their contents
+                                                 have been committed */
+} virDomainBlockCommitFlags;
+
+int virDomainBlockCommit(virDomainPtr dom, const char *disk, const char *base,
+                         const char *top, unsigned long bandwidth,
+                         unsigned int flags);

Hm, I'm always wondering how things would be if we'd use libvirt "objects" instead of strings for doing such things:

We could use a virStorageVolPtrs for the arguments but we would need to have a way to use storage volumes not present in libvirt's pools. (We would need a way to wrap them somehow into our storage objects).

But anyways, with the current state a the objects are still looked up by matching name or UUID so this solution is probably more versatile and requires less layers of code to traverse, so I'm fine with it.

+

  /* Block I/O throttling support */

diff --git a/src/driver.h b/src/driver.h
index bb470fe..063bbbf 100644
--- a/src/driver.h
+++ b/src/driver.h
@@ -832,6 +832,10 @@ typedef int
      (*virDrvDomainBlockRebase)(virDomainPtr dom, const char *path,
                                 const char *base, unsigned long bandwidth,
                                 unsigned int flags);
+typedef int
+    (*virDrvDomainBlockCommit)(virDomainPtr dom, const char *disk,
+                               const char *base, const char *top,
+                               unsigned long bandwidth, unsigned int flags);

  typedef int
      (*virDrvSetKeepAlive)(virConnectPtr conn,
@@ -1071,6 +1075,7 @@ struct _virDriver {
      virDrvDomainBlockJobSetSpeed        domainBlockJobSetSpeed;
      virDrvDomainBlockPull               domainBlockPull;
      virDrvDomainBlockRebase             domainBlockRebase;
+    virDrvDomainBlockCommit             domainBlockCommit;
      virDrvSetKeepAlive                  setKeepAlive;
      virDrvConnectIsAlive                isAlive;
      virDrvNodeSuspendForDuration        nodeSuspendForDuration;
diff --git a/src/libvirt.c b/src/libvirt.c
index 9848993..41ecda1 100644
--- a/src/libvirt.c
+++ b/src/libvirt.c
@@ -19219,6 +19219,111 @@ error:


  /**
+ * virDomainBlockCommit:
+ * @dom: pointer to domain object
+ * @disk: path to the block device, or device shorthand
+ * @base: path to backing file to merge into, or NULL for default
+ * @top: path to file within backing chain that contains data to be merged,
+ *       or NULL to merge all possible data
+ * @bandwidth: (optional) specify commit bandwidth limit in MiB/s
+ * @flags: bitwise-OR of virDomainBlockCommitFlags
+ *
+ * Commit changes that were made to temporary top-level files within a disk
+ * image backing file chain into a lower-level base file.  In other words,
+ * take all the difference between @base and @top, and update @base to contain
+ * that difference; after the commit, any portion of the chain that previously
+ * depended on @top will now depend on @base, and all files after @base up
+ * to and including @top will now be invalidated.  A typical use of this
+ * command is to reduce the length of a backing file chain after taking an
+ * external disk snapshot.
+ *
+ * This command starts a long-running commit block job, whose status may
+ * be tracked by virDomainBlockJobInfo() with a job type of
+ * VIR_DOMAIN_BLOCK_JOB_TYPE_COMMIT, and the operation can be aborted with
+ * virDomainBlockJobAbort().  When finished, an asynchronous event is
+ * raised to indicate the final status, and the job no longer exists.  If
+ * the job is aborted, it is up to the hypervisor whether starting a new
+ * job will resume from the same point, or start over.
+ *
+ * Be aware that this command may invalidate files even if it is aborted;
+ * the user is cautioned against relying on the contents of invalidated
+ * files such as @top without manually rebasing those files to use a
+ * backing file of a read-only copy of @base prior to the point where the
+ * commit operation was restarted (although such a rebase cannot be safely
+ * done until the commit has successfully completed).  As a convenience,
+ * if @flags contains VIR_DOMAIN_BLOCK_COMMIT_DELETE, this command will
+ * unlink all files that were invalidated, after the commit successfully
+ * completes.
+ *
+ * By default, if @base is NULL, the bottom of the backing chain will be
+ * the commit target; if @flags contains VIR_DOMAIN_BLOCK_COMMIT_SHALLOW,
+ * then the immediate backing file of @top will be used instead.  If @top
+ * is NULL, the active image at the top of the chain will be used.  Some
+ * hypervisors place restrictions on how much can be committed, and might
+ * fail if @base is not the immediate backing file of @top, or if @top is
+ * in use by a running domain, or if @top is not the top-most file.
+ *
+ * The @disk parameter is either an unambiguous source name of the
+ * block device (the <source file='...'/> sub-element, such as
+ * "/path/to/image"), or the device target shorthand (the
+ * <target dev='...'/> sub-element, such as "xvda").  Valid names
+ * can be found by calling virDomainGetXMLDesc() and inspecting
+ * elements within //domain/devices/disk.
+ *
+ * The maximum bandwidth (in MiB/s) that will be used to do the commit can be
+ * specified with the bandwidth parameter.  If set to 0, libvirt will choose a
+ * suitable default.  Some hypervisors do not support this feature and will
+ * return an error if bandwidth is not 0; in this case, it might still be
+ * possible for a later call to virDomainBlockJobSetSpeed() to succeed.
+ * The actual speed can be determined with virDomainGetBlockJobInfo().
+ *
+ * Returns 0 if the operation has started, -1 on failure.

Wow, exhaustive docs!

+ */
+int virDomainBlockCommit(virDomainPtr dom, const char *disk,
+                         const char *base, const char *top,
+                         unsigned long bandwidth, unsigned int flags)
+{
+    virConnectPtr conn;
+
+    VIR_DOMAIN_DEBUG(dom, "disk=%s, base=%s, top=%s, bandwidth=%lu, flags=%x",
+                     disk, NULLSTR(base), NULLSTR(top), bandwidth, flags);
+
+    virResetLastError();
+
+    if (!VIR_IS_CONNECTED_DOMAIN(dom)) {
+        virLibDomainError(VIR_ERR_INVALID_DOMAIN, __FUNCTION__);
+        virDispatchError(NULL);
+        return -1;
+    }
+    conn = dom->conn;
+
+    if (dom->conn->flags & VIR_CONNECT_RO) {
+        virLibDomainError(VIR_ERR_OPERATION_DENIED, __FUNCTION__);
+        goto error;
+    }
+
+    virCheckNonNullArgGoto(disk, error);
+    if (flags & VIR_DOMAIN_BLOCK_COMMIT_SHALLOW)
+        virCheckNullArgGoto(base, error);
+
+    if (conn->driver->domainBlockCommit) {
+        int ret;
+        ret = conn->driver->domainBlockCommit(dom, disk, base, top, bandwidth,
+                                              flags);
+        if (ret < 0)
+            goto error;
+        return ret;
+    }
+
+    virLibDomainError(VIR_ERR_NO_SUPPORT, __FUNCTION__);
+
+error:
+    virDispatchError(dom->conn);
+    return -1;
+}
+
+
+/**
   * virDomainOpenGraphics:
   * @dom: pointer to domain object
   * @idx: index of graphics config to open
diff --git a/src/libvirt_public.syms b/src/libvirt_public.syms
index 28b92ad..d965c7f 100644
--- a/src/libvirt_public.syms
+++ b/src/libvirt_public.syms
@@ -562,6 +562,7 @@ LIBVIRT_0.10.2 {
          virConnectListAllNWFilters;
          virConnectListAllSecrets;
          virConnectListAllStoragePools;
+        virDomainBlockCommit;
          virNodeGetMemoryParameters;
          virNodeSetMemoryParameters;
          virStoragePoolListAllVolumes;


This patch as well as the API looks fine from my point of view and contains a ton of documentation, so ACK if nobody else objects.

Peter


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