scanning: open devs rw when rescanning for write

When vg_read rescans devices with the intention of
writing the VG, the label rescan can open the devs
RW so they do not need to be closed and reopened
RW in dev_write_bytes.

lib/cache/lvmcache.c

@@ -772,7 +772,7 @@ next:
  * to that VG after a scan.
  */
 
-int lvmcache_label_rescan_vg(struct cmd_context *cmd, const char *vgname, const char *vgid)
+static int _label_rescan_vg(struct cmd_context *cmd, const char *vgname, const char *vgid, int rw)
 {
 	struct dm_list devs;
 	struct device_list *devl, *devl2;
@@ -804,6 +804,9 @@ int lvmcache_label_rescan_vg(struct cmd_context *cmd, const char *vgname, const
 	/* FIXME: should we also rescan unused_duplicate_devs for devs
 	   being rescanned here and then repeat resolving the duplicates? */
 
+	if (rw)
+		label_scan_devs_rw(cmd, cmd->filter, &devs);
+	else
 		label_scan_devs(cmd, cmd->filter, &devs);
 
 	dm_list_iterate_items_safe(devl, devl2, &devs) {
@@ -819,6 +822,16 @@ int lvmcache_label_rescan_vg(struct cmd_context *cmd, const char *vgname, const
 	return 1;
 }
 
+int lvmcache_label_rescan_vg(struct cmd_context *cmd, const char *vgname, const char *vgid)
+{
+	return _label_rescan_vg(cmd, vgname, vgid, 0);
+}
+
+int lvmcache_label_rescan_vg_rw(struct cmd_context *cmd, const char *vgname, const char *vgid)
+{
+	return _label_rescan_vg(cmd, vgname, vgid, 1);
+}
+
 /*
  * Uses label_scan to populate lvmcache with 'vginfo' struct for each VG
  * and associated 'info' structs for those VGs.  Only VG summary information

lib/cache/lvmcache.h

@@ -71,6 +71,7 @@ void lvmcache_destroy(struct cmd_context *cmd, int retain_orphans, int reset);
 
 int lvmcache_label_scan(struct cmd_context *cmd);
 int lvmcache_label_rescan_vg(struct cmd_context *cmd, const char *vgname, const char *vgid);
+int lvmcache_label_rescan_vg_rw(struct cmd_context *cmd, const char *vgname, const char *vgid);
 
 /* Add/delete a device */
 struct lvmcache_info *lvmcache_add(struct labeller *labeller, const char *pvid,

lib/label/label.c

@@ -1118,7 +1118,37 @@ int label_scan_devs(struct cmd_context *cmd, struct dev_filter *f, struct dm_lis
 
 	_scan_list(cmd, f, devs, NULL);
 
-	/* FIXME: this function should probably fail if any devs couldn't be scanned */
+	return 1;
+}
+
+/*
+ * This function is used when the caller plans to write to the devs, so opening
+ * them RW during rescan avoids needing to close and reopen with WRITE in
+ * dev_write_bytes.
+ */
+
+int label_scan_devs_rw(struct cmd_context *cmd, struct dev_filter *f, struct dm_list *devs)
+{
+	struct device_list *devl;
+
+	if (!scan_bcache) {
+		if (!_setup_bcache(0))
+			return 0;
+	}
+
+	dm_list_iterate_items(devl, devs) {
+		if (_in_bcache(devl->dev)) {
+			bcache_invalidate_fd(scan_bcache, devl->dev->bcache_fd);
+			_scan_dev_close(devl->dev);
+		}
+		/*
+		 * With this flag set, _scan_dev_open() done by
+		 * _scan_list() will do open RW
+		 */
+		devl->dev->flags |= DEV_BCACHE_WRITE;
+	}
+
+	_scan_list(cmd, f, devs, NULL);
 
 	return 1;
 }

lib/label/label.h

@@ -104,6 +104,7 @@ extern struct bcache *scan_bcache;
 
 int label_scan(struct cmd_context *cmd);
 int label_scan_devs(struct cmd_context *cmd, struct dev_filter *f, struct dm_list *devs);
+int label_scan_devs_rw(struct cmd_context *cmd, struct dev_filter *f, struct dm_list *devs);
 int label_scan_devs_excl(struct dm_list *devs);
 void label_scan_invalidate(struct device *dev);
 void label_scan_invalidate_lv(struct cmd_context *cmd, struct logical_volume *lv);

lib/metadata/metadata-exported.h

@@ -184,8 +184,9 @@
 #define READ_ALLOW_EXPORTED	0x00020000U
 #define READ_OK_NOTFOUND	0x00040000U
 #define READ_WARN_INCONSISTENT	0x00080000U
-#define READ_FOR_UPDATE		0x00100000U /* A meta-flag, useful with toollib for_each_* functions. */
+#define READ_FOR_UPDATE		0x00100000U /* command tells vg_read it plans to write the vg */
 #define PROCESS_SKIP_SCAN	0x00200000U /* skip lvmcache_label_scan in process_each_pv */
+#define READ_FOR_ACTIVATE	0x00400000U /* command tells vg_read it plans to activate the vg */
 
 /* vg_read returns these in error_flags */
 #define FAILED_NOT_ENABLED	0x00000001U

lib/metadata/metadata.c

@@ -4476,7 +4476,8 @@ void vg_write_commit_bad_mdas(struct cmd_context *cmd, struct volume_group *vg)
 static struct volume_group *_vg_read(struct cmd_context *cmd,
 				     const char *vgname,
 				     const char *vgid,
-				     unsigned precommitted)
+				     unsigned precommitted,
+				     int writing)
 {
 	const struct format_type *fmt = cmd->fmt;
 	struct format_instance *fid = NULL;
@@ -4530,7 +4531,10 @@ static struct volume_group *_vg_read(struct cmd_context *cmd,
 	 * we can also skip the rescan in that case.
 	 */
 	if (!cmd->can_use_one_scan || lvmcache_scan_mismatch(cmd, vgname, vgid)) {
-		log_debug_metadata("Rescanning devices for %s", vgname);
+		log_debug_metadata("Rescanning devices for %s %s", vgname, writing ? "rw" : "");
+		if (writing)
+			lvmcache_label_rescan_vg_rw(cmd, vgname, vgid);
+		else
 			lvmcache_label_rescan_vg(cmd, vgname, vgid);
 	} else {
 		log_debug_metadata("Skipped rescanning devices for %s", vgname);
@@ -4752,6 +4756,7 @@ struct volume_group *vg_read(struct cmd_context *cmd, const char *vg_name, const
 	int missing_pv_flag = 0;
 	uint32_t failure = 0;
 	int writing = (read_flags & READ_FOR_UPDATE);
+	int activating = (read_flags & READ_FOR_ACTIVATE);
 
 	if (is_orphan_vg(vg_name)) {
 		log_very_verbose("Reading orphan VG %s", vg_name);
@@ -4766,13 +4771,23 @@ struct volume_group *vg_read(struct cmd_context *cmd, const char *vg_name, const
 		return NULL;
 	}
 
-	if (!lock_vol(cmd, vg_name, writing ? LCK_VG_WRITE : LCK_VG_READ, NULL)) {
+	/*
+	 * When a command is reading the VG with the intention of eventually
+	 * writing it, it passes the READ_FOR_UPDATE flag.  This causes vg_read
+	 * to acquire an exclusive VG lock, and causes vg_read to do some more
+	 * checks, e.g. that the VG is writable and not exported.  It also
+	 * means that when the label scan is repeated on the VG's devices, the
+	 * VG's PVs can be reopened read-write when rescanning in anticipation
+	 * of needing to write to them.
+	 */
+
+	if (!lock_vol(cmd, vg_name, (writing || activating) ? LCK_VG_WRITE : LCK_VG_READ, NULL)) {
 		log_error("Can't get lock for %s", vg_name);
 		failure |= FAILED_LOCKING;
 		goto_bad;
 	}
 
-	if (!(vg = _vg_read(cmd, vg_name, vgid, 0))) {
+	if (!(vg = _vg_read(cmd, vg_name, vgid, 0, writing))) {
 		/* Some callers don't care if the VG doesn't exist and don't want an error message. */
 		if (!(read_flags & READ_OK_NOTFOUND))
 			log_error("Volume group \"%s\" not found", vg_name);
@@ -4883,30 +4898,37 @@ struct volume_group *vg_read(struct cmd_context *cmd, const char *vg_name, const
 		goto_bad;
 	}
 
-	if (writing && !(read_flags & READ_ALLOW_EXPORTED) && vg_is_exported(vg)) {
+	/*
+	 * If the command intends to write or activate the VG, there are
+	 * additional restrictions.  FIXME: These restrictions should
+	 * probably be checked/applied after vg_read returns.
+	 */
+	if (writing || activating) {
+		if (!(read_flags & READ_ALLOW_EXPORTED) && vg_is_exported(vg)) {
 			log_error("Volume group %s is exported", vg->name);
 			failure |= FAILED_EXPORTED;
 			goto_bad;
 		}
 
-	if (writing && !(vg->status & LVM_WRITE)) {
+		if (!(vg->status & LVM_WRITE)) {
 			log_error("Volume group %s is read-only", vg->name);
 			failure |= FAILED_READ_ONLY;
 			goto_bad;
 		}
 
-	if (!cmd->handles_missing_pvs && (missing_pv_dev || missing_pv_flag) && writing) {
+		if (!cmd->handles_missing_pvs && (missing_pv_dev || missing_pv_flag)) {
 			log_error("Cannot change VG %s while PVs are missing.", vg->name);
 			log_error("See vgreduce --removemissing and vgextend --restoremissing.");
 			failure |= FAILED_NOT_ENABLED;
 			goto_bad;
 		}
 
-	if (!cmd->handles_unknown_segments && vg_has_unknown_segments(vg) && writing) {
+		if (!cmd->handles_unknown_segments && vg_has_unknown_segments(vg)) {
 			log_error("Cannot change VG %s with unknown segments in it!", vg->name);
 			failure |= FAILED_NOT_ENABLED; /* FIXME new failure code here? */
 			goto_bad;
 		}
+	}
 
 	/*
 	 * When we are reading the VG with the intention of writing it,

tools/lvchange.c

@@ -1435,7 +1435,7 @@ int lvchange_activate_cmd(struct cmd_context *cmd, int argc, char **argv)
 	} else /* Component LVs might be active, support easy deactivation */
 		cmd->process_component_lvs = 1;
 
-	ret = process_each_lv(cmd, argc, argv, NULL, NULL, READ_FOR_UPDATE,
+	ret = process_each_lv(cmd, argc, argv, NULL, NULL, READ_FOR_ACTIVATE,
 			      NULL, &_lvchange_activate_check, &_lvchange_activate_single);
 
 	if (ret != ECMD_PROCESSED)

tools/pvscan.c

@@ -900,7 +900,7 @@ static int _pvscan_aa(struct cmd_context *cmd, struct pvscan_aa_params *pp,
 		return ECMD_PROCESSED;
 	}
 
-	ret = process_each_vg(cmd, 0, NULL, NULL, vgnames, READ_FOR_UPDATE, 0, handle, _pvscan_aa_single);
+	ret = process_each_vg(cmd, 0, NULL, NULL, vgnames, READ_FOR_ACTIVATE, 0, handle, _pvscan_aa_single);
 
 	destroy_processing_handle(cmd, handle);
 

tools/vgchange.c

@@ -800,8 +800,10 @@ int vgchange(struct cmd_context *cmd, int argc, char **argv)
 			cmd->lockd_vg_enforce_sh = 1;
 	}
 
-	if (update || arg_is_set(cmd, activate_ARG))
+	if (update)
 		flags |= READ_FOR_UPDATE;
+	else if (arg_is_set(cmd, activate_ARG))
+		flags |= READ_FOR_ACTIVATE;
 
 	if (!(handle = init_processing_handle(cmd, NULL))) {
 		log_error("Failed to initialize processing handle.");