[PATCH 1/2 v3] e2fsck: Discard only unused parts of inode table

[Lukas Czerner <lczerner@redhat.com>]

When calling e2fsck with '-E discard' option it might happen that
valid inodes are discarded accidentally. This is because we just
discard the part of inode table which lies past the free inode count.
This is terribly wrong (sorry!).

This patch fixes it so only the free parts of an inode table
is discarded, leaving used inodes intact. This was tested with highly
fragmented inode tables with block size 4k and 1k.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Reported-by: Phillip Susi <psusi@ubuntu.com>
---
v2: reworked so that we comply with inode number counting and adjust
    start in the e2fsck_discard_inodes(). Add some comments
v3: Update commit description

 e2fsck/pass5.c |   82 ++++++++++++++++++++++++++++++++++++++++---------------
 1 files changed, 59 insertions(+), 23 deletions(-)

diff --git a/e2fsck/pass5.c b/e2fsck/pass5.c
index 1e836e3..f70928f 100644
--- a/e2fsck/pass5.c
+++ b/e2fsck/pass5.c
@@ -94,6 +94,43 @@ static void e2fsck_discard_blocks(e2fsck_t ctx, io_manager manager,
 		ctx->options &= ~E2F_OPT_DISCARD;
 }
 
+/*
+ * This will try to discard number 'count' inodes starting at
+ * inode number 'start'. Note that 'start' is a inode number and
+ * henc it is counted from 1, it means that we need to adjust it
+ * by -1 in this function to compute right offset in the
+ * inode table.
+ */
+static void e2fsck_discard_inodes(e2fsck_t ctx, int group,
+				  int start, int count)
+{
+	ext2_filsys fs = ctx->fs;
+	blk64_t blk, num;
+	int orig = count;
+
+	if ((ctx->options & E2F_OPT_NO) || !(ctx->options & E2F_OPT_DISCARD))
+		return;
+
+	/*
+	 * Start is inode number which starts counting from 1,
+	 * so we need to adjust it.
+	 */
+	start -= 1;
+
+	/*
+	 * We can discard only blocks containing only unused
+	 * inodes in the table.
+	 */
+	blk = DIV_ROUND_UP(start,
+		EXT2_INODES_PER_BLOCK(fs->super));
+	count -= (blk * EXT2_INODES_PER_BLOCK(fs->super) - start);
+	blk += ext2fs_inode_table_loc(fs, group);
+	num = count / EXT2_INODES_PER_BLOCK(fs->super);
+
+	if (num > 0)
+		e2fsck_discard_blocks(ctx, fs->io->manager, blk, num);
+}
+
 #define NO_BLK ((blk64_t) -1)
 
 static void print_bitmap_problem(e2fsck_t ctx, int problem,
@@ -435,6 +472,7 @@ static void check_inode_bitmaps(e2fsck_t ctx)
 	int		skip_group = 0;
 	int		redo_flag = 0;
 	io_manager	manager = ctx->fs->io->manager;
+	unsigned long long	first_free = fs->super->s_inodes_per_group + 1;
 
 	clear_problem_context(&pctx);
 	free_array = (int *) e2fsck_allocate_memory(ctx,
@@ -497,6 +535,7 @@ redo_counts:
 				 * are 0, count the free inode,
 				 * skip the current block group.
 				 */
+				first_free = 1;
 				inodes = fs->super->s_inodes_per_group - 1;
 				group_free = inodes;
 				free_inodes += inodes;
@@ -561,50 +600,47 @@ redo_counts:
 		ctx->options &= ~E2F_OPT_DISCARD;
 
 do_counts:
+		inodes++;
 		if (bitmap) {
 			if (ext2fs_test_inode_bitmap2(ctx->inode_dir_map, i))
 				dirs_count++;
+			if (inodes > first_free) {
+				e2fsck_discard_inodes(ctx, group, first_free,
+						      inodes - first_free);
+				first_free = fs->super->s_inodes_per_group + 1;
+			}
 		} else if (!skip_group || csum_flag) {
 			group_free++;
 			free_inodes++;
+			if (first_free > inodes)
+				first_free = inodes;
 		}
 
-		inodes++;
 		if ((inodes == fs->super->s_inodes_per_group) ||
 		    (i == fs->super->s_inodes_count)) {
-
-			free_array[group] = group_free;
-			dir_array[group] = dirs_count;
-
-			/* Discard inode table */
-			if (ctx->options & E2F_OPT_DISCARD) {
-				blk64_t used_blks, blk, num;
-
-				used_blks = DIV_ROUND_UP(
-					(EXT2_INODES_PER_GROUP(fs->super) -
-					group_free),
-					EXT2_INODES_PER_BLOCK(fs->super));
-
-				blk = ext2fs_inode_table_loc(fs, group) +
-				      used_blks;
-				num = fs->inode_blocks_per_group -
-				      used_blks;
-				e2fsck_discard_blocks(ctx, manager, blk, num);
-			}
-
+			/*
+			 * If the last inode is free, we can discard it as well.
+			 */
+			if (inodes >= first_free)
+				e2fsck_discard_inodes(ctx, group, first_free,
+						      inodes - first_free + 1);
 			/*
 			 * If discard zeroes data and the group inode table
 			 * was not zeroed yet, set itable as zeroed
 			 */
 			if ((ctx->options & E2F_OPT_DISCARD) &&
-			    (io_channel_discard_zeroes_data(fs->io)) &&
+			    !(ctx->options & E2F_OPT_NO) &&
+			    io_channel_discard_zeroes_data(fs->io) &&
 			    !(ext2fs_bg_flags_test(fs, group,
-						  EXT2_BG_INODE_ZEROED))) {
+						   EXT2_BG_INODE_ZEROED))) {
 				ext2fs_bg_flags_set(fs, group,
 						    EXT2_BG_INODE_ZEROED);
 				ext2fs_group_desc_csum_set(fs, group);
 			}
 
+			first_free = fs->super->s_inodes_per_group + 1;
+			free_array[group] = group_free;
+			dir_array[group] = dirs_count;
 			group ++;
 			inodes = 0;
 			skip_group = 0;
-- 
1.7.4.4