Grow: store a link to current backup file in /run/mdadm or similar.

Subsequent patch will allow the background part of "mdadm --grow" to
be run from systemd.  This can require the passing of a backup file
name.
To do this, store that name as a symlink in /run/mdadm (or MAP_DIR)
and look for it when appropriate.

It might be useful to also store the name across reboot, but that
would be a different patch.  We would need to use the uuid to identify
it, and store it in stable storage.

Signed-off-by: NeilBrown <neilb@suse.de>

Assemble.c

@@ -1680,6 +1680,8 @@ try_again:
 			pr_err(":%s has an active reshape - checking "
 			       "if critical section needs to be restored\n",
 			       chosen_name);
+		if (!c->backup_file)
+			c->backup_file = locate_backup(content->sys_name);
 		enable_fds(bestcnt/2);
 		for (i = 0; i < bestcnt/2; i++) {
 			int j = best[i*2];
@@ -1892,7 +1894,7 @@ int assemble_container_content(struct supertype *st, int mdfd,
 		int spare = content->array.raid_disks + expansion;
 		if (restore_backup(st, content,
 				   working,
-				   spare, c->backup_file, c->verbose) == 1)
+				   spare, &c->backup_file, c->verbose) == 1)
 			return 1;
 
 		err = sysfs_set_str(content, NULL,

Grow.c

@@ -41,7 +41,7 @@ int restore_backup(struct supertype *st,
 		   struct mdinfo *content,
 		   int working_disks,
 		   int next_spare,
-		   char *backup_file,
+		   char **backup_filep,
 		   int verbose)
 {
 	int i;
@@ -49,6 +49,7 @@ int restore_backup(struct supertype *st,
 	struct mdinfo *dev;
 	int err;
 	int disk_count = next_spare + working_disks;
+	char *backup_file = *backup_filep;
 
 	dprintf("Called restore_backup()\n");
 	fdlist = xmalloc(sizeof(int) * disk_count);
@@ -70,6 +71,11 @@ int restore_backup(struct supertype *st,
 			fdlist[next_spare++] = fd;
 	}
 
+	if (!backup_file) {
+		backup_file = locate_backup(content->sys_name);
+		*backup_filep = backup_file;
+	}
+
 	if (st->ss->external && st->ss->recover_backup)
 		err = st->ss->recover_backup(st, content);
 	else
@@ -886,6 +892,7 @@ int reshape_open_backup_file(char *backup_file,
 			     long blocks,
 			     int *fdlist,
 			     unsigned long long *offsets,
+			     char *sys_name,
 			     int restart)
 {
 	/* Return 1 on success, 0 on any form of failure */
@@ -933,6 +940,12 @@ int reshape_open_backup_file(char *backup_file,
 		return 0;
 	}
 
+	if (!restart && strncmp(backup_file, MAP_DIR, strlen(MAP_DIR)) != 0) {
+		char *bu = make_backup(sys_name);
+		symlink(backup_file, bu);
+		free(bu);
+	}
+
 	return 1;
 }
 
@@ -2843,6 +2856,10 @@ static int reshape_array(char *container, int fd, char *devname,
 			       devname);
 			goto release;
 		}
+
+		if (!backup_file)
+			backup_file = locate_backup(sra->sys_name);
+
 		goto started;
 	}
 	/* The container is frozen but the array may not be.
@@ -3172,6 +3189,7 @@ started:
 			if (!reshape_open_backup_file(backup_file, fd, devname,
 						      (signed)blocks,
 						      fdlist+d, offsets+d,
+						      sra->sys_name,
 						      restart)) {
 				goto release;
 			}
@@ -3292,8 +3310,15 @@ started:
 	free(fdlist);
 	free(offsets);
 
-	if (backup_file && done)
+	if (backup_file && done) {
+		char *bul;
 		unlink(backup_file);
+		bul = make_backup(sra->sys_name);
+		if (bul) {
+			unlink(bul);
+			free(bul);
+		}
+	}
 	if (!done) {
 		abort_reshape(sra);
 		goto out;
@@ -4879,3 +4904,28 @@ int Grow_continue(int mdfd, struct supertype *st, struct mdinfo *info,
 
 	return ret_val;
 }
+
+char *make_backup(char *name)
+{
+	char *base = "backup_file-";
+	int len;
+	char *fname;
+
+	len = strlen(MAP_DIR) + 1 + strlen(base) + strlen(name)+1;
+	fname = xmalloc(len);
+	sprintf(fname, "%s/%s%s", MAP_DIR, base, name);
+	return fname;
+}
+
+char *locate_backup(char *name)
+{
+	char *fl = make_backup(name);
+	struct stat stb;
+
+	if (stat(fl, &stb) == 0 &&
+	    S_ISREG(stb.st_mode))
+		return fl;
+
+	free(fl);
+	return NULL;
+}

mdadm.h

@@ -585,9 +585,12 @@ extern int reshape_open_backup_file(char *backup,
 				    long blocks,
 				    int *fdlist,
 				    unsigned long long *offsets,
+				    char *sysfs_name,
 				    int restart);
 extern unsigned long compute_backup_blocks(int nchunk, int ochunk,
 					   unsigned int ndata, unsigned int odata);
+extern char *locate_backup(char *name);
+extern char *make_backup(char *name);
 
 extern int save_stripes(int *source, unsigned long long *offsets,
 			int raid_disks, int chunk_size, int level, int layout,
@@ -1196,7 +1199,7 @@ extern int restore_backup(struct supertype *st,
 			  struct mdinfo *content,
 			  int working_disks,
 			  int spares,
-			  char *backup_file,
+			  char **backup_filep,
 			  int verbose);
 extern int Grow_continue_command(char *devname, int fd,
 				 char *backup_file, int verbose);