zfs-mount-generator: generate zvol dependencies

Signed-off-by: Antonio Russo <aerusso@aerusso.net>

cmd/zed/zed.d/history_event-zfs-list-cacher.sh.in

@@ -74,6 +74,13 @@ PROPS="name,mountpoint,canmount,atime,relatime,devices,exec\
 ,org.openzfs.systemd:nofail,org.openzfs.systemd:ignore"
 
 "${ZFS}" list -H -t filesystem -o "${PROPS}" -r "${ZEVENT_POOL}" > "${FSLIST_TMP}"
+"${ZFS}" list -H -t volume -o "name,org.openzfs.systemd:ignore" -r "${ZEVENT_POOL}" |
+    IFS="	" while read -r name ignore ; do
+        [ "${ignore}" = "on" ] && continue
+
+        # fake "zvol" mountpoint
+        printf '%s\tzvol\n' "${name}" >> "${FSLIST_TMP}"
+done
 
 # Sort the output so that it is stable
 sort "${FSLIST_TMP}" -o "${FSLIST_TMP}"

etc/systemd/system-generators/Makefile.am

@@ -1,5 +1,7 @@
 include $(top_srcdir)/config/Rules.am
 
+AM_CPPFLAGS += -DSYSTEMDUNITDIR=\"$(systemdunitdir)\"
+
 systemdgenerator_PROGRAMS = \
 	zfs-mount-generator
 

etc/systemd/system-generators/zfs-mount-generator.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017 Antonio Russo <antonio.e.russo@gmail.com>
+ * Copyright (c) 2017, 2022 Antonio Russo <aerusso@aerusso.net>
  * Copyright (c) 2020 InsanePrawn <insane.prawny@gmail.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
@@ -56,6 +56,7 @@
 #define	PROGNAME "zfs-mount-generator"
 #define	FSLIST SYSCONFDIR "/zfs/zfs-list.cache"
 #define	ZFS SBINDIR "/zfs"
+#define	ZVOL_TARGET_DIR "zfs-volumes.target.requires"
 
 #define	OUTPUT_HEADER \
 	"# Automatically generated by " PROGNAME "\n" \
@@ -194,7 +195,57 @@ fopenat(int dirfd, const char *pathname, int flags,
 }
 
 static int
-line_worker(char *line, const char *cachefile)
+line_worker_volume(char *line, int *zvol_depdir_fd)
+{
+	char *toktmp;
+	const char *dataset = strtok_r(line, "\t", &toktmp);
+
+	if (*zvol_depdir_fd < 0) {
+		(void) mkdirat(destdir_fd, ZVOL_TARGET_DIR, 0755);
+		*zvol_depdir_fd = openat(destdir_fd, ZVOL_TARGET_DIR,
+		    O_PATH | O_DIRECTORY | O_CLOEXEC);
+		if (*zvol_depdir_fd < 0) {
+			fprintf(stderr, PROGNAME "[%d]: "
+			    "can't open %s/" ZVOL_TARGET_DIR ": %s\n",
+			    getpid(), destdir, strerror(errno));
+			return 1;
+		}
+	}
+
+	char *zvol_service = systemd_escape(dataset, "zfs-volume@", ".service");
+	if (zvol_service == NULL)
+	    return 1;
+
+	int retval = 0;
+
+	if (symlinkat(SYSTEMDUNITDIR "/zfs-volume@.service",
+	    *zvol_depdir_fd, zvol_service) == -1) {
+		struct stat stbuf;
+
+		if ((fstatat(*zvol_depdir_fd, zvol_service, &stbuf, AT_SYMLINK_NOFOLLOW) == 0) &&
+		    ((stbuf.st_mode & S_IFMT) == S_IFLNK)) {
+			fprintf(stderr, PROGNAME "[%d]: %s: "
+			    "symlink at %s under "
+			    "%s/" ZVOL_TARGET_DIR " already exists: Skipping.\n",
+			    getpid(), dataset, zvol_service, destdir);
+		} else {
+			fprintf(stderr, PROGNAME "[%d]: %s: "
+			"couldn't symlink at %s under "
+			"%s/" ZVOL_TARGET_DIR ": %s\n",
+			getpid(), dataset, zvol_service,
+			destdir, strerror(errno));
+			retval = 1;
+		}
+	}
+
+	free(zvol_service);
+
+	return retval;
+}
+
+
+static int
+line_worker_filesystem(char *line, const char *cachefile)
 {
 	int ret = 0;
 	void *tofree_all[8];
@@ -771,6 +822,7 @@ int
 main(int argc, char **argv)
 {
 	struct timespec time_init = {};
+	int zvol_depdir_fd = -1;
 	clock_gettime(CLOCK_MONOTONIC_RAW, &time_init);
 
 	{
@@ -895,13 +947,32 @@ main(int argc, char **argv)
 
 			char *canmount = line;
 			canmount += strcspn(canmount, "\t");
+
+			/* This SHOULD contain the dataset name */
+			if (canmount == line) {
+				/* Throw an error if we didn't find anything */
+				fprintf(stderr, PROGNAME "[%d]: %s: not enough tokens!\n",
+				    getpid(), cachent->d_name);
+				ret = 1;
+				continue;
+			}
+
 			canmount += strspn(canmount, "\t");
+
+			/* This is the second attribute in the zfs-list file */
+			if ((strncmp(canmount, "zvol", 4) == 0)
+			   && ( (canmount[4] == '\0') || (canmount[4] == '\t') )) {
+				/* special case of zvol */
+				ret |= line_worker_volume(line, &zvol_depdir_fd);
+				continue;
+			}
+
 			canmount += strcspn(canmount, "\t");
 			canmount += strspn(canmount, "\t");
 			bool canmount_on = strncmp(canmount, "on", 2) == 0;
 
 			if (canmount_on)
-				ret |= line_worker(line, cachent->d_name);
+				ret |= line_worker_filesystem(line, cachent->d_name);
 			else {
 				if (filename == NULL)
 					filename =
@@ -928,11 +999,15 @@ main(int argc, char **argv)
 	}
 	free(line);
 
+	if (zvol_depdir_fd >= 0) {
+	    (void) close(zvol_depdir_fd);
+	}
+
 	while (lines_canmount_not_on) {
 		struct line *l = lines_canmount_not_on;
 		lines_canmount_not_on = l->next;
 
-		ret |= line_worker(l->line, l->fname);
+		ret |= line_worker_filesystem(l->line, l->fname);
 		if (FREE_STATICS) {
 			free(l->line);
 			free(l);

etc/systemd/system/Makefile.am

@@ -10,6 +10,7 @@ systemdunit_DATA = \
 	zfs-mount.service \
 	zfs-share.service \
 	zfs-volume-wait.service \
+	zfs-volume@.service \
 	zfs-import.target \
 	zfs-volumes.target \
 	zfs.target \

etc/systemd/system/zfs-volume@.service.in

@@ -0,0 +1,10 @@
+[Unit]
+Description=Wait for ZFS volume %I
+Documentation=man:zfs-mount-generator(8)
+After=zfs-import.target
+ConditionPathIsDirectory=/sys/module/zfs
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=@bindir@/zvol_wait %I