[25/31] libext2fs: find/alloc a range of empty blocks

diff --git a/lib/ext2fs/alloc.c b/lib/ext2fs/alloc.c
index 9901ca5..4c3b620 100644
--- a/lib/ext2fs/alloc.c
+++ b/lib/ext2fs/alloc.c
@@ -26,6 +26,16 @@ 
 #include "ext2_fs.h"
 #include "ext2fs.h"
 
+#define min(a, b) ((a) < (b) ? (a) : (b))
+
+#undef DEBUG
+
+#ifdef DEBUG
+# define dbg_printf(f, a...)  do {printf(f, ## a); fflush(stdout); } while (0)
+#else
+# define dbg_printf(f, a...)
+#endif
+
 /*
  * Clear the uninit block bitmap flag if necessary
  */
@@ -346,3 +356,134 @@  no_blocks:
 		group = group & ~((1 << (log_flex)) - 1);
 	return ext2fs_group_first_block2(fs, group);
 }
+
+/*
+ * Starting at _goal_, scan around the filesystem to find a run of free blocks
+ * that's at least _len_ blocks long.  Possible flags:
+ * - EXT2_NEWRANGE_EXACT_GOAL: The range of blocks must start at _goal_.
+ * - EXT2_NEWRANGE_MIN_LENGTH: do not return a allocation shorter than _len_.
+ * - EXT2_NEWRANGE_ZERO_BLOCKS: Zero blocks pblk to pblk+plen before returning.
+ *
+ * The starting block is returned in _pblk_ and the length is returned via
+ * _plen_.  The blocks are not marked in the bitmap; the caller must mark
+ * however much of the returned run they actually use, hopefully via
+ * ext2fs_block_alloc_stats_range().
+ *
+ * This function can return a range that is longer than what was requested.
+ */
+errcode_t ext2fs_new_range(ext2_filsys fs, int flags, blk64_t goal,
+			   blk64_t len, ext2fs_block_bitmap map, blk64_t *pblk,
+			   blk64_t *plen)
+{
+	errcode_t retval;
+	blk64_t start, end, b;
+	int looped = 0;
+	blk64_t max_blocks = ext2fs_blocks_count(fs->super);
+
+	dbg_printf("%s: flags=0x%x goal=%llu len=%llu\n", __func__, flags,
+		   goal, len);
+	EXT2_CHECK_MAGIC(fs, EXT2_ET_MAGIC_EXT2FS_FILSYS);
+	if (len == 0 || (flags & ~EXT2_NEWRANGE_ALL_FLAGS))
+		return EXT2_ET_INVALID_ARGUMENT;
+	if (!map)
+		map = fs->block_map;
+	if (!map)
+		return EXT2_ET_NO_BLOCK_BITMAP;
+	if (!goal || goal >= ext2fs_blocks_count(fs->super))
+		goal = fs->super->s_first_data_block;
+
+	start = goal;
+	while (!looped || start <= goal) {
+		retval = ext2fs_find_first_zero_block_bitmap2(map, start,
+							      max_blocks - 1,
+							      &start);
+		if (retval == ENOENT) {
+			/*
+			 * If there are no free blocks beyond the starting
+			 * point, try scanning the whole filesystem, unless the
+			 * user told us only to allocate from _goal_, or if
+			 * we're already scanning the whole filesystem.
+			 */
+			if (flags & EXT2_NEWRANGE_FIXED_GOAL ||
+			    start == fs->super->s_first_data_block)
+				goto fail;
+			start = fs->super->s_first_data_block;
+			continue;
+		} else if (retval)
+			goto errout;
+
+		if (flags & EXT2_NEWRANGE_FIXED_GOAL && start != goal)
+			goto fail;
+
+		b = min(start + len - 1, max_blocks - 1);
+		retval =  ext2fs_find_first_set_block_bitmap2(map, start, b,
+							      &end);
+		if (retval == ENOENT)
+			end = b + 1;
+		else if (retval)
+			goto errout;
+
+		if (!(flags & EXT2_NEWRANGE_MIN_LENGTH) ||
+		    (end - start) >= len) {
+			/* Success! */
+			*pblk = start;
+			*plen = end - start;
+			dbg_printf("%s: new_range goal=%llu--%llu "
+				   "blk=%llu--%llu %llu\n",
+				   __func__, goal, goal + len - 1,
+				   *pblk, *pblk + *plen - 1, *plen);
+
+			for (b = start; b < end;
+			     b += fs->super->s_blocks_per_group)
+				clear_block_uninit(fs,
+						ext2fs_group_of_blk2(fs, b));
+			return 0;
+		}
+
+		if (flags & EXT2_NEWRANGE_FIXED_GOAL)
+			goto fail;
+		start = end;
+		if (start >= max_blocks) {
+			if (looped)
+				goto fail;
+			looped = 1;
+			start = fs->super->s_first_data_block;
+		}
+	}
+
+fail:
+	retval = EXT2_ET_BLOCK_ALLOC_FAIL;
+errout:
+	return retval;
+}
+
+errcode_t ext2fs_alloc_range(ext2_filsys fs, int flags, blk64_t goal,
+			     blk_t len, blk64_t *ret)
+{
+	int newr_flags = EXT2_NEWRANGE_MIN_LENGTH;
+	errcode_t retval;
+	blk64_t plen;
+
+	EXT2_CHECK_MAGIC(fs, EXT2_ET_MAGIC_EXT2FS_FILSYS);
+	if (len == 0 || (flags & ~EXT2_ALLOCRANGE_ALL_FLAGS))
+		return EXT2_ET_INVALID_ARGUMENT;
+
+	if (flags & EXT2_ALLOCRANGE_FIXED_GOAL)
+		newr_flags |= EXT2_NEWRANGE_FIXED_GOAL;
+
+	retval = ext2fs_new_range(fs, newr_flags, goal, len, NULL, ret, &plen);
+	if (retval)
+		return retval;
+
+	if (plen < len)
+		return EXT2_ET_BLOCK_ALLOC_FAIL;
+
+	if (flags & EXT2_ALLOCRANGE_ZERO_BLOCKS) {
+		retval = ext2fs_zero_blocks2(fs, *ret, len, NULL, NULL);
+		if (retval)
+			return retval;
+	}
+
+	ext2fs_block_alloc_stats_range(fs, *ret, len, +1);
+	return retval;
+}
diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h
index e117441..bfe0ecf 100644
--- a/lib/ext2fs/ext2fs.h
+++ b/lib/ext2fs/ext2fs.h
@@ -693,6 +693,17 @@  extern void ext2fs_set_alloc_block_callback(ext2_filsys fs,
 							      blk64_t *ret));
 blk64_t ext2fs_find_inode_goal(ext2_filsys fs, ext2_ino_t ino,
 			       struct ext2_inode *inode, blk64_t lblk);
+#define EXT2_NEWRANGE_FIXED_GOAL	(0x1)
+#define EXT2_NEWRANGE_MIN_LENGTH	(0x2)
+#define EXT2_NEWRANGE_ALL_FLAGS		(0x3)
+errcode_t ext2fs_new_range(ext2_filsys fs, int flags, blk64_t goal,
+			   blk64_t len, ext2fs_block_bitmap map, blk64_t *pblk,
+			   blk64_t *plen);
+#define EXT2_ALLOCRANGE_FIXED_GOAL	(0x1)
+#define EXT2_ALLOCRANGE_ZERO_BLOCKS	(0x2)
+#define EXT2_ALLOCRANGE_ALL_FLAGS	(0x3)
+errcode_t ext2fs_alloc_range(ext2_filsys fs, int flags, blk64_t goal,
+			     blk_t len, blk64_t *ret);
 
 /* alloc_sb.c */
 extern int ext2fs_reserve_super_and_bgd(ext2_filsys fs,