lvreduce: check for file system that cannot be reduced

New command line option --detectfs y|n  (default y)

lib/device/dev-type.c

@@ -725,6 +725,39 @@ int get_fs_block_size(struct device *dev, uint32_t *fs_block_size)
 }
 #endif
 
+#ifdef BLKID_WIPING_SUPPORT
+int get_fs_can_reduce(const char *pathname, int *fs_can_reduce, char *fs_buf, int fs_buf_len)
+{
+	char *fs_str = NULL;
+
+	if ((fs_str = blkid_get_tag_value(NULL, "TYPE", pathname))) {
+		if (fs_buf && fs_buf_len)
+			strncpy(fs_buf, fs_str, fs_buf_len-1);
+
+		log_debug("Found blkid filesystem TYPE %s on %s", fs_str, pathname);
+
+		if (fs_str && !strcmp(fs_str, "ext4"))
+			*fs_can_reduce = 1;
+		else
+			*fs_can_reduce = 0;
+
+		free(fs_str);
+		return 1;
+	} else {
+		log_debug("No blkid filesystem TYPE found for %s", pathname);;
+		*fs_can_reduce = 0;
+		return 0;
+	}
+}
+#else
+int get_fs_can_reduce(const char *pathname, int *fs_can_reduce, char *fs_buf, int fs_buf_len)
+{
+	log_warn("Disabled blkid for fs type check.");
+	*fs_can_reduce = 0;
+	return 0;
+}
+#endif
+
 #ifdef BLKID_WIPING_SUPPORT
 
 static inline int _type_in_flag_list(const char *type, uint32_t flag_list)

lib/device/dev-type.h

@@ -102,4 +102,6 @@ int dev_is_lv(struct device *dev);
 
 int get_fs_block_size(struct device *dev, uint32_t *fs_block_size);
 
+int get_fs_can_reduce(const char *pathname, int *fs_can_reduce, char *fs_buf, int fs_buf_len);
+
 #endif

lib/metadata/lv_manip.c

@@ -6050,6 +6050,42 @@ int lv_resize(struct logical_volume *lv,
 	    (pvh != &vg->pvs))
 		log_print_unless_silent("Ignoring PVs on command line when reducing.");
 
+	if (lp->detectfs) {
+		char pathname[PATH_MAX];
+		char *dmname;
+		char fs_buf[16] = {0};
+		int fs_can_reduce = 0;
+
+		/* if lv is not active, activate it */
+		if (!lv_is_active(lv)) {
+			if (!activate_lv(cmd, lv)) {
+				log_error("Failed to activate %s for --detectfs.", display_lvname(lv));
+				return 0;
+			}
+			if (!sync_local_dev_names(cmd))
+				return_0;
+			activated = 1;
+		}
+
+		if (!(dmname = dm_build_dm_name(cmd->mem, vg->name, lv->name, NULL)))
+			return_0;
+
+		if (dm_snprintf(pathname, sizeof(pathname), "%s/%s", dm_dir(), dmname) < 0)
+			return_0;
+
+		/* use blkid to check fs type, we know which types can reduce */
+		if (!get_fs_can_reduce(pathname, &fs_can_reduce, fs_buf, sizeof(fs_buf))) {
+			log_error("Failed to find file system type for --detectfs.");
+			goto bad;
+		}
+
+		if (!fs_can_reduce) {
+			log_error("Found file system type %s that cannot be reduced (from --detectfs).",
+				  fs_buf[0] ? fs_buf : "unknown");
+			goto bad;
+		}
+	}
+
 	/* Request confirmation before operations that are often mistakes. */
 	/* aux_lv never resize fs */
 	if ((lp->resizefs || (lp->resize == LV_REDUCE)) &&

lib/metadata/metadata-exported.h

@@ -687,6 +687,7 @@ struct lvresize_params {
 	int nosync;
 	int nofsck;
 	int resizefs;
+	int detectfs;
 
 	unsigned mirrors;
 	uint32_t stripes;

tools/args.h

@@ -155,6 +155,10 @@ arg(cachesize_ARG, '\0', "cachesize", sizemb_VAL, 0, 0,
 arg(check_ARG, '\0', "check", 0, 0, 0,
     "Check the content of the devices file.\n")
 
+arg(detectfs_ARG, '\0', "detectfs", bool_VAL, 0, 0,
+    "Check the LV for file system information. This activates the LV if\n"
+    "needed so that the LV can be read to look for fs superblocks.\n")
+
 arg(commandprofile_ARG, '\0', "commandprofile", string_VAL, 0, 0,
     "The command profile to use for command configuration.\n"
     "See \\fBlvm.conf\\fP(5) for more information about profiles.\n")

tools/command-lines.in

@@ -1449,7 +1449,7 @@ DESC: Remove the devices file entry for the given PVID.
 
 lvreduce --size NSizeMB LV
 OO: --autobackup Bool, --force, --nofsck, --noudevsync,
---reportformat ReportFmt, --resizefs
+--reportformat ReportFmt, --resizefs, --detectfs Bool
 ID: lvreduce_general
 
 ---
@@ -1479,7 +1479,7 @@ lvresize --size SSizeMB LV
 OO: --alloc Alloc, --autobackup Bool, --force,
 --nofsck, --nosync, --noudevsync, --reportformat ReportFmt, --resizefs,
 --stripes Number, --stripesize SizeKB, --poolmetadatasize PSizeMB,
---type SegType
+--type SegType, --detectfs Bool
 OP: PV ...
 ID: lvresize_by_size
 DESC: Resize an LV by a specified size.
@@ -1488,7 +1488,7 @@ lvresize LV PV ...
 OO: --alloc Alloc, --autobackup Bool, --force,
 --nofsck, --nosync, --noudevsync,
 --reportformat ReportFmt, --resizefs, --stripes Number, --stripesize SizeKB,
---type SegType
+--type SegType, --detectfs Bool
 ID: lvresize_by_pv
 DESC: Resize an LV by specified PV extents.
 

tools/lvresize.c

@@ -39,6 +39,13 @@ static int _lvresize_params(struct cmd_context *cmd, int argc, char **argv,
 	else
 		lp->resize = LV_ANY;
 
+	if (lp->resize == LV_REDUCE) {
+		if (arg_is_set(cmd, detectfs_ARG))
+			lp->detectfs = arg_int_value(cmd, detectfs_ARG, 1);
+		else
+			lp->detectfs = 1;
+	}
+
 	lp->sign = lp->poolmetadata_sign = SIGN_NONE;
 
 	if ((lp->use_policies = arg_is_set(cmd, usepolicies_ARG))) {