1 files changed, 254 insertions, 1 deletions

diff --git a/cmds-filesystem.c b/cmds-filesystem.c
index 800aa4dc..b44a6553 100644
--- a/cmds-filesystem.c
+++ b/cmds-filesystem.c
@@ -1271,14 +1271,264 @@ static int cmd_defrag(int argc, char **argv)
 }
 
 static const char * const cmd_resize_usage[] = {
-	"btrfs filesystem resize [devid:][+/-]<newsize>[kKmMgGtTpPeE]|[devid:]max <path>",
+	"btrfs filesystem resize [devid:][+/-]<newsize>[kKmMgGtTpPeE]|[devid:]max|[devid:]get_min_size <path>",
 	"Resize a filesystem",
 	"If 'max' is passed, the filesystem will occupy all available space",
 	"on the device 'devid'.",
+	"If 'get_min_size' is passed, return the minimum size the device can",
+	"be shrunk to.",
 	"[kK] means KiB, which denotes 1KiB = 1024B, 1MiB = 1024KiB, etc.",
 	NULL
 };
 
+struct dev_extent_elem {
+	u64 start;
+	/* inclusive end */
+	u64 end;
+	struct list_head list;
+};
+
+static int add_dev_extent(struct list_head *list,
+			  const u64 start, const u64 end,
+			  const int append)
+{
+	struct dev_extent_elem *e;
+
+	e = malloc(sizeof(*e));
+	if (!e)
+		return -ENOMEM;
+
+	e->start = start;
+	e->end = end;
+
+	if (append)
+		list_add_tail(&e->list, list);
+	else
+		list_add(&e->list, list);
+
+	return 0;
+}
+
+static void free_dev_extent_list(struct list_head *list)
+{
+	while (!list_empty(list)) {
+		struct dev_extent_elem *e;
+
+		e = list_first_entry(list, struct dev_extent_elem, list);
+		list_del(&e->list);
+		free(e);
+	}
+}
+
+static int hole_includes_sb_mirror(const u64 start, const u64 end)
+{
+	int i;
+	int ret = 0;
+
+	for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
+		u64 bytenr = btrfs_sb_offset(i);
+
+		if (bytenr >= start && bytenr <= end) {
+			ret = 1;
+			break;
+		}
+	}
+
+	return ret;
+}
+
+static void adjust_dev_min_size(struct list_head *extents,
+				struct list_head *holes,
+				u64 *min_size)
+{
+	/*
+	 * If relocation of the block group of a device extent must happen (see
+	 * below) scratch space is used for the relocation. So track here the
+	 * size of the largest device extent that has to be relocated. We track
+	 * only the largest and not the sum of the sizes of all relocated block
+	 * groups because after each block group is relocated the running
+	 * transaction is committed so that pinned space is released.
+	 */
+	u64 scratch_space = 0;
+
+	/*
+	 * List of device extents is sorted by descending order of the extent's
+	 * end offset. If some extent goes beyond the computed minimum size,
+	 * which initially matches the sum of the lenghts of all extents,
+	 * we need to check if the extent can be relocated to an hole in the
+	 * device between [0, *min_size[ (which is what the resize ioctl does).
+	 */
+	while (!list_empty(extents)) {
+		struct dev_extent_elem *e;
+		struct dev_extent_elem *h;
+		int found = 0;
+		u64 extent_len;
+		u64 hole_len = 0;
+
+		e = list_first_entry(extents, struct dev_extent_elem, list);
+		if (e->end <= *min_size)
+			break;
+
+		/*
+		 * Our extent goes beyond the computed *min_size. See if we can
+		 * find a hole large enough to relocate it to. If not we must stop
+		 * and set *min_size to the end of the extent.
+		 */
+		extent_len = e->end - e->start + 1;
+		list_for_each_entry(h, holes, list) {
+			hole_len = h->end - h->start + 1;
+			if (hole_len >= extent_len) {
+				found = 1;
+				break;
+			}
+		}
+
+		if (!found) {
+			*min_size = e->end + 1;
+			break;
+		}
+
+		/*
+		 * If the hole found contains the location for a superblock
+		 * mirror, we are pessimistic and require allocating one
+		 * more extent of the same size. This is because the block
+		 * group could be in the worst case used by a single extent
+		 * with a size >= (block_group.length - superblock.size).
+		 */
+		if (hole_includes_sb_mirror(h->start,
+					    h->start + extent_len - 1))
+			*min_size += extent_len;
+
+		if (hole_len > extent_len) {
+			h->start += extent_len;
+		} else {
+			list_del(&h->list);
+			free(h);
+		}
+
+		list_del(&e->list);
+		free(e);
+
+		if (extent_len > scratch_space)
+			scratch_space = extent_len;
+	}
+
+	if (scratch_space) {
+		*min_size += scratch_space;
+		/*
+		 * Chunk allocation requires inserting/updating items in the
+		 * chunk tree, so often this can lead to the need of allocating
+		 * a new system chunk too, which has a maximum size of 32Mb.
+		 */
+		*min_size += 32 * 1024 * 1024;
+	}
+}
+
+static int get_min_size(int fd, DIR *dirstream, const char *amount)
+{
+	int ret = 1;
+	char *p = strstr(amount, ":");
+	u64 devid = 1;
+	/*
+	 * Device allocations starts at 1Mb or at the value passed through the
+	 * mount option alloc_start if it's bigger than 1Mb. The alloc_start
+	 * option is used for debugging and testing only, and recently the
+	 * possibility of deprecating/removing it has been discussed, so we
+	 * ignore it here.
+	 */
+	u64 min_size = 1 * 1024 * 1024ull;
+	struct btrfs_ioctl_search_args args;
+	struct btrfs_ioctl_search_key *sk = &args.key;
+	u64 last_pos = (u64)-1;
+	LIST_HEAD(extents);
+	LIST_HEAD(holes);
+
+	if (p && sscanf(amount, "%llu:get_min_size", &devid) != 1) {
+		fprintf(stderr, "Invalid parameter: %s\n", amount);
+		goto out;
+	}
+
+	memset(&args, 0, sizeof(args));
+	sk->tree_id = BTRFS_DEV_TREE_OBJECTID;
+	sk->min_objectid = devid;
+	sk->max_objectid = devid;
+	sk->max_type = BTRFS_DEV_EXTENT_KEY;
+	sk->min_type = BTRFS_DEV_EXTENT_KEY;
+	sk->min_offset = 0;
+	sk->max_offset = (u64)-1;
+	sk->min_transid = 0;
+	sk->max_transid = (u64)-1;
+	sk->nr_items = 4096;
+
+	while (1) {
+		int i;
+		struct btrfs_ioctl_search_header *sh;
+		unsigned long off = 0;
+
+		ret = ioctl(fd, BTRFS_IOC_TREE_SEARCH, &args);
+		if (ret < 0) {
+			fprintf(stderr,
+				"Error invoking tree search ioctl: %s\n",
+				strerror(errno));
+			ret = 1;
+			goto out;
+		}
+
+		if (sk->nr_items == 0)
+			break;
+
+		for (i = 0; i < sk->nr_items; i++) {
+			struct btrfs_dev_extent *extent;
+			u64 len;
+
+			sh = (struct btrfs_ioctl_search_header *)(args.buf +
+								  off);
+			off += sizeof(*sh);
+			extent = (struct btrfs_dev_extent *)(args.buf + off);
+			off += sh->len;
+
+			sk->min_objectid = sh->objectid;
+			sk->min_type = sh->type;
+			sk->min_offset = sh->offset + 1;
+
+			if (sh->objectid != devid ||
+			    sh->type != BTRFS_DEV_EXTENT_KEY)
+				continue;
+
+			len = btrfs_stack_dev_extent_length(extent);
+			min_size += len;
+			ret = add_dev_extent(&extents, sh->offset,
+					     sh->offset + len - 1, 0);
+
+			if (!ret && last_pos != (u64)-1 &&
+			    last_pos != sh->offset)
+				ret = add_dev_extent(&holes, last_pos,
+						     sh->offset - 1, 1);
+			if (ret) {
+				fprintf(stderr, "Error: %s\n", strerror(-ret));
+				ret = 1;
+				goto out;
+			}
+
+			last_pos = sh->offset + len;
+		}
+
+		if (sk->min_type != BTRFS_DEV_EXTENT_KEY ||
+		    sk->min_objectid != devid)
+			break;
+	}
+
+	adjust_dev_min_size(&extents, &holes, &min_size);
+	printf("%llu bytes (%s)\n", min_size, pretty_size(min_size));
+	ret = 0;
+out:
+	close_file_or_dir(fd, dirstream);
+	free_dev_extent_list(&extents);
+	free_dev_extent_list(&holes);
+
+	return ret;
+}
+
 static int cmd_resize(int argc, char **argv)
 {
 	struct btrfs_ioctl_vol_args	args;
@@ -1320,6 +1570,9 @@ static int cmd_resize(int argc, char **argv)
 		return 1;
 	}
 
+	if (strstr(amount, "get_min_size"))
+		return get_min_size(fd, dirstream, amount);
+
 	printf("Resize '%s' of '%s'\n", path, amount);
 	memset(&args, 0, sizeof(args));
 	strncpy_null(args.name, amount);