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[lvm-devel] [PATCH 1/2] lvconvert --merge @tag support



Switch lvconvert's --merge code over to using process_each_lv().  Doing
so adds support for a single 'lvconvert --merge' to start merging
multiple LVs (which includes @tag expansion).

Add 'lvconvert --merge @tag' testing to test/t-snapshot-merge.sh

The lvconvert.c implementation requires rereading the VG each iteration
of process_each_lv().  Otherwise a stale VG instance associated with
the LV passed to lvconvert_single_merge() would result in stale VG
metadata being written back out to disk.  This overwrote new metadata
that was written when a previous snapshot LV finished merging (via
lvconvert_poll).  This is only an issue when merging multiple LVs that
share the same VG (a single VG is typical for most LVM configurations on
system disks).

In the end this new support is very useful for performing a "system
rollback" that requires multiple snapshot LVs be merged to their
respective origin LV.

The yum-utils 'fs-snapshot' plugin tags all snapshot LVs that it creates
with a common 'snapshot_tag' that is unique to the yum transaction.
Rolling back a yum transaction, that created LVM snapshots with the tag
'yum_20100129133223', is as simple as:
  lvconvert --merge @yum_20100129133223

Signed-off-by: Mike Snitzer <snitzer redhat com>
---
 test/t-snapshot-merge.sh |   11 +++
 tools/lvconvert.c        |  159 +++++++++++++++++++++++++++++++++++++----------
 2 files changed, 139 insertions(+), 31 deletions(-)

Index: lvm2/tools/lvconvert.c
===================================================================
--- lvm2.orig/tools/lvconvert.c
+++ lvm2/tools/lvconvert.c
@@ -55,7 +55,10 @@ static int _lvconvert_name_params(struct
 	char *ptr;
 	const char *vg_name = NULL;
 
-	if (lp->snapshot && !lp->merge) {
+	if (lp->merge)
+		return 1;
+
+	if (lp->snapshot) {
 		if (!*pargc) {
 			log_error("Please specify a logical volume to act as "
 				  "the snapshot origin.");
@@ -105,7 +108,7 @@ static int _lvconvert_name_params(struct
 	if (!apply_lvname_restrictions(lp->lv_name))
 		return_0;
 
-	if (*pargc && (lp->snapshot || lp->merge)) {
+	if (*pargc && lp->snapshot) {
 		log_error("Too many arguments provided for snapshots");
 		return 0;
 	}
@@ -1205,8 +1208,8 @@ out:
 	return r;
 }
 
-static int lvconvert_single(struct cmd_context *cmd, struct logical_volume *lv,
-			    void *handle)
+static int _lvconvert_single(struct cmd_context *cmd, struct logical_volume *lv,
+			     void *handle)
 {
 	struct lvconvert_params *lp = handle;
 
@@ -1276,60 +1279,154 @@ static int lvconvert_single(struct cmd_c
 	return ECMD_PROCESSED;
 }
 
-int lvconvert(struct cmd_context * cmd, int argc, char **argv)
+static struct logical_volume *get_logical_volume(struct cmd_context *cmd,
+						 const char *vg_name,
+						 const char *lv_name)
 {
+	/*
+	 * Returns NULL if the requested LV doesn't exist;
+	 * otherwise the caller must vg_release(lv->vg)
+	 * - it is also up to the caller to unlock_vg() as needed
+	 */
 	struct volume_group *vg;
 	struct lv_list *lvl;
-	struct lvconvert_params lp;
-	int ret = ECMD_FAILED;
+	struct logical_volume* lv = NULL;
+
+	log_verbose("Checking for existing volume group \"%s\"", vg_name);
+
+	vg = vg_read_for_update(cmd, vg_name, NULL, 0);
+	if (vg_read_error(vg)) {
+		vg_release(vg);
+		return NULL;
+	}
+
+	if (!(lvl = find_lv_in_vg(vg, lv_name))) {
+		log_error("Logical volume \"%s\" not found in "
+			  "volume group \"%s\"", lv_name, vg_name);
+		unlock_and_release_vg(cmd, vg, vg_name);
+		return NULL;
+	}
+	lv = lvl->lv;
+
+	return lv;
+}
+
+static int poll_logical_volume(struct cmd_context *cmd, struct logical_volume *lv,
+			       int wait_completion)
+{
 	struct lvinfo info;
-	int saved_ignore_suspended_devices = ignore_suspended_devices();
 
-	if (!_read_params(&lp, cmd, argc, argv)) {
-		stack;
-		return EINVALID_CMD_LINE;
+	if (!lv_info(cmd, lv, &info, 1, 0) || !info.exists) {
+		log_print("Conversion starts after activation.");
+		return ECMD_PROCESSED;
 	}
+	return lvconvert_poll(cmd, lv, wait_completion ? 0 : 1U);
+}
+
+static int lvconvert_single(struct cmd_context *cmd, struct lvconvert_params *lp)
+{
+	struct volume_group *vg;
+	struct lv_list *lvl;
+	int ret = ECMD_FAILED;
+	int saved_ignore_suspended_devices = ignore_suspended_devices();
 
 	if (arg_count(cmd, repair_ARG)) {
 		init_ignore_suspended_devices(1);
 		cmd->handles_missing_pvs = 1;
 	}
 
-	log_verbose("Checking for existing volume group \"%s\"", lp.vg_name);
+	log_verbose("Checking for existing volume group \"%s\"", lp->vg_name);
 
-	vg = vg_read_for_update(cmd, lp.vg_name, NULL, 0);
+	vg = vg_read_for_update(cmd, lp->vg_name, NULL, 0);
 	if (vg_read_error(vg))
 		goto out;
 
-	if (!(lvl = find_lv_in_vg(vg, lp.lv_name))) {
+	if (!(lvl = find_lv_in_vg(vg, lp->lv_name))) {
 		log_error("Logical volume \"%s\" not found in "
-			  "volume group \"%s\"", lp.lv_name, lp.vg_name);
+			  "volume group \"%s\"", lp->lv_name, lp->vg_name);
 		goto bad;
 	}
 
-	if (lp.pv_count) {
-		if (!(lp.pvh = create_pv_list(cmd->mem, vg, lp.pv_count,
-					      lp.pvs, 0)))
+	if (lp->pv_count) {
+		if (!(lp->pvh = create_pv_list(cmd->mem, vg, lp->pv_count,
+					      lp->pvs, 0)))
 			goto_bad;
 	} else
-		lp.pvh = &vg->pvs;
-
-	lp.lv_to_poll = lvl->lv;
-	ret = lvconvert_single(cmd, lvl->lv, &lp);
+		lp->pvh = &vg->pvs;
 
+	lp->lv_to_poll = lvl->lv;
+	ret = _lvconvert_single(cmd, lvl->lv, lp);
 bad:
-	unlock_vg(cmd, lp.vg_name);
+	unlock_vg(cmd, lp->vg_name);
 
-	if (ret == ECMD_PROCESSED && lp.need_polling) {
-		if (!lv_info(cmd, lp.lv_to_poll, &info, 1, 0) || !info.exists) {
-			log_print("Conversion starts after activation");
-			goto out;
-		}
-		ret = lvconvert_poll(cmd, lp.lv_to_poll,
-				     lp.wait_completion ? 0 : 1U);
-	}
+	if (ret == ECMD_PROCESSED && lp->need_polling)
+		ret = poll_logical_volume(cmd, lp->lv_to_poll,
+					  lp->wait_completion);
 out:
 	init_ignore_suspended_devices(saved_ignore_suspended_devices);
 	vg_release(vg);
 	return ret;
 }
+
+static int lvconvert_single_merge(struct cmd_context *cmd, struct logical_volume *lv,
+				  void *handle)
+{
+	struct lvconvert_params *lp = handle;
+	const char *vg_name = NULL;
+	struct logical_volume *refreshed_lv = NULL;
+	int ret;
+
+	/*
+	 * FIXME can't trust lv's VG to be current given that caller
+	 * is process_each_lv() -- poll_logical_volume() may have
+	 * already updated the VG's metadata in an earlier iteration.
+	 * - preemptively drop the VG lock, as is needed for
+	 *   poll_logical_volume(), refresh LV (and VG in the process).
+	 */
+	vg_name = lv->vg->name;
+	unlock_vg(cmd, vg_name);
+	refreshed_lv = get_logical_volume(cmd, vg_name, lv->name);
+	if (!refreshed_lv)
+		return ECMD_FAILED;
+
+	lp->lv_to_poll = refreshed_lv;
+	ret = _lvconvert_single(cmd, refreshed_lv, lp);
+
+	if (ret == ECMD_PROCESSED && lp->need_polling) {
+		/*
+		 * Must drop VG lock, because lvconvert_poll() needs it,
+		 * then reacquire it after polling completes
+		 */
+		unlock_vg(cmd, vg_name);
+
+		ret = poll_logical_volume(cmd, lp->lv_to_poll,
+					  lp->wait_completion);
+
+		/* use LCK_VG_WRITE to match lvconvert()'s READ_FOR_UPDATE */
+		if (!lock_vol(cmd, vg_name, LCK_VG_WRITE)) {
+			log_error("ABORTING: Can't relock VG for %s "
+				  "after polling finished", vg_name);
+			ret = ECMD_FAILED;
+		}
+	}
+
+	vg_release(refreshed_lv->vg);
+
+	return ret;
+}
+
+int lvconvert(struct cmd_context * cmd, int argc, char **argv)
+{
+	struct lvconvert_params lp;
+
+	if (!_read_params(&lp, cmd, argc, argv)) {
+		stack;
+		return EINVALID_CMD_LINE;
+	}
+
+	if (lp.merge)
+		return process_each_lv(cmd, argc, argv, READ_FOR_UPDATE, &lp,
+				       &lvconvert_single_merge);
+
+	return lvconvert_single(cmd, &lp);
+}
Index: lvm2/test/t-snapshot-merge.sh
===================================================================
--- lvm2.orig/test/t-snapshot-merge.sh
+++ lvm2/test/t-snapshot-merge.sh
@@ -77,6 +77,17 @@ lvs -a
 lvconvert --merge $vg/$(snap_lv_name_ $lv1)
 lvremove -f $vg/$lv1
 
+# test merging multiple snapshots that share the same tag
+setup_merge $vg $lv1
+setup_merge $vg $lv2
+lvs -a
+lvchange --addtag this_is_a_test $vg/$(snap_lv_name_ $lv1)
+lvchange --addtag this_is_a_test $vg/$(snap_lv_name_ $lv2)
+lvconvert --merge @this_is_a_test
+lvs | not grep $(snap_lv_name_ $lv1)
+lvs | not grep $(snap_lv_name_ $lv2)
+lvremove -f $vg/$lv1
+lvremove -f $vg/$lv2
 
 # FIXME following tests would need to poll merge progress, via periodic lvs?
 # Background processes don't lend themselves to lvm testsuite...


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