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Date:	Mon,  5 Mar 2012 08:49:33 +0100
From:	Lukas Czerner <lczerner@...hat.com>
To:	linux-ext4@...r.kernel.org
Cc:	tytso@....edu, sandeen@...hat.com,
	Lukas Czerner <lczerner@...hat.com>
Subject: [PATCH 1/4] e2fsck: Discard only unused parts of inode table

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@...hat.com>
Reported-by: Phillip Susi <psusi@...ntu.com>
---
 e2fsck/pass5.c |   90 +++++++++++++++++++++++++++++++++++++++++--------------
 1 files changed, 67 insertions(+), 23 deletions(-)

diff --git a/e2fsck/pass5.c b/e2fsck/pass5.c
index 1e836e3..ee73dd5 100644
--- a/e2fsck/pass5.c
+++ b/e2fsck/pass5.c
@@ -94,6 +94,52 @@ 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' within the 'group'. Note that 'start'
+ * is 1-based, it means that we need to adjust it by -1 in this
+ * function to compute right offset in the particular 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;
+
+	/*
+	 * Sanity check for 'start'
+	 */
+	if ((start < 1) || (start > EXT2_INODES_PER_GROUP(fs->super))) {
+		printf("PROGRAMMING ERROR: Got start %d outside of group %d!"
+		       " Disabling discard\n",
+			start, group);
+		ctx->options &= ~E2F_OPT_DISCARD;
+	}
+
+	if ((ctx->options & E2F_OPT_NO) || !(ctx->options & E2F_OPT_DISCARD))
+		return;
+
+	/*
+	 * Start is inode number within the group 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 +481,7 @@ 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 +544,7 @@ 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 +609,46 @@ 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)) &&
+			    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

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