libsquashfs: remove the default block writer alignment feature

The idea of the block align feature was to allow micro-managing that
some files are forcefully aligned to 1k/4k ("device block") boundaries,
hoping to improve access time at the cost of data density. The feature
was not exposed in the tools for a long time and eventuall added to the
sort file. Measurement and experimentation showed, that it in fact
worsened the read performance on a test system with an old micro SD
card as the bottle neck.

The feature is removed, and if needed, can be brought back simply by
wrapping/sub-classing the default block writer, if need be..

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

3 files changed, 8 insertions, 56 deletions

diff --git a/lib/common/src/writer/init.c b/lib/common/src/writer/init.c
index 497fc6e..fe5fcc5 100644
--- a/lib/common/src/writer/init.c
+++ b/lib/common/src/writer/init.c
@@ -120,8 +120,7 @@ int sqfs_writer_init(sqfs_writer_t *sqfs, const sqfs_writer_cfg_t *wrcfg)
 	if (ret > 0)
 		sqfs->super.flags |= SQFS_FLAG_COMPRESSOR_OPTIONS;
 
-	sqfs->blkwr = sqfs_block_writer_create(sqfs->outfile,
-					       wrcfg->devblksize, 0);
+	sqfs->blkwr = sqfs_block_writer_create(sqfs->outfile, 0);
 	if (sqfs->blkwr == NULL) {
 		perror("creating block writer");
 		goto fail_uncmp;
diff --git a/lib/sqfs/src/block_processor/backend.c b/lib/sqfs/src/block_processor/backend.c
index b443c9d..acff7f5 100644
--- a/lib/sqfs/src/block_processor/backend.c
+++ b/lib/sqfs/src/block_processor/backend.c
@@ -202,8 +202,7 @@ static int process_completed_fragment(sqfs_block_processor_t *proc,
 		offset = 0;
 		proc->frag_block = frag;
 		proc->frag_block->index = index;
-		proc->frag_block->flags &=
-			(SQFS_BLK_DONT_COMPRESS | SQFS_BLK_ALIGN);
+		proc->frag_block->flags &= SQFS_BLK_DONT_COMPRESS;
 		proc->frag_block->flags |= SQFS_BLK_FRAGMENT_BLOCK;
 	} else {
 		index = proc->frag_block->index;
@@ -214,8 +213,7 @@ static int process_completed_fragment(sqfs_block_processor_t *proc,
 
 		proc->frag_block->size += frag->size;
 		proc->frag_block->flags |=
-			(frag->flags &
-			 (SQFS_BLK_DONT_COMPRESS | SQFS_BLK_ALIGN));
+			(frag->flags & SQFS_BLK_DONT_COMPRESS);
 	}
 
 	if (proc->frag_tbl != NULL) {
diff --git a/lib/sqfs/src/block_writer.c b/lib/sqfs/src/block_writer.c
index a5135bc..c747079 100644
--- a/lib/sqfs/src/block_writer.c
+++ b/lib/sqfs/src/block_writer.c
@@ -36,7 +36,6 @@ typedef struct {
 	sqfs_file_t *file;
 
 	array_t blocks;
-	size_t devblksz;
 
 	size_t file_start;
 
@@ -79,9 +78,6 @@ static int deduplicate_blocks(block_writer_default_t *wr, sqfs_u32 flags, sqfs_u
 
 	for (i = 0; i < wr->file_start; ++i) {
 		for (j = 0; j < count; ++j) {
-			if (blocks[i + j].hash == 0)
-				break;
-
 			if (blocks[i + j].hash !=
 			    blocks[wr->file_start + j].hash)
 				break;
@@ -119,33 +115,6 @@ static int deduplicate_blocks(block_writer_default_t *wr, sqfs_u32 flags, sqfs_u
 	return wr->file->truncate(wr->file, sz);
 }
 
-static int align_file(block_writer_default_t *wr, sqfs_u32 flags)
-{
-	void *padding;
-	sqfs_u64 size;
-	size_t diff;
-	int ret;
-
-	if (!(flags & SQFS_BLK_ALIGN))
-		return 0;
-
-	size = wr->file->get_size(wr->file);
-	diff = size % wr->devblksz;
-	if (diff == 0)
-		return 0;
-
-	padding = calloc(1, diff);
-	if (padding == 0)
-		return SQFS_ERROR_ALLOC;
-
-	ret = wr->file->write_at(wr->file, size, padding, diff);
-	free(padding);
-	if (ret)
-		return ret;
-
-	return store_block_location(wr, size, 0, 0);
-}
-
 static void block_writer_destroy(sqfs_object_t *wr)
 {
 	sqfs_drop(((block_writer_default_t *)wr)->file);
@@ -161,14 +130,8 @@ static int write_data_block(sqfs_block_writer_t *base, void *user,
 	int err;
 	(void)user;
 
-	if (flags & (SQFS_BLK_FIRST_BLOCK | SQFS_BLK_FRAGMENT_BLOCK)) {
-		err = align_file(wr, flags);
-		if (err)
-			return err;
-
-		if (flags & SQFS_BLK_FIRST_BLOCK)
-			wr->file_start = wr->blocks.used;
-	}
+	if (flags & SQFS_BLK_FIRST_BLOCK)
+		wr->file_start = wr->blocks.used;
 
 	*location = wr->file->get_size(wr->file);
 
@@ -186,14 +149,8 @@ static int write_data_block(sqfs_block_writer_t *base, void *user,
 			return err;
 	}
 
-	if (flags & (SQFS_BLK_LAST_BLOCK | SQFS_BLK_FRAGMENT_BLOCK)) {
-		err = align_file(wr, flags);
-		if (err)
-			return err;
-
-		if (flags & SQFS_BLK_LAST_BLOCK)
-			return deduplicate_blocks(wr, flags, location);
-	}
+	if (flags & SQFS_BLK_LAST_BLOCK)
+		return deduplicate_blocks(wr, flags, location);
 
 	return 0;
 }
@@ -203,8 +160,7 @@ static sqfs_u64 get_block_count(const sqfs_block_writer_t *wr)
 	return ((const block_writer_default_t *)wr)->blocks.used;
 }
 
-sqfs_block_writer_t *sqfs_block_writer_create(sqfs_file_t *file,
-					      size_t devblksz, sqfs_u32 flags)
+sqfs_block_writer_t *sqfs_block_writer_create(sqfs_file_t *file, sqfs_u32 flags)
 {
 	block_writer_default_t *wr;
 
@@ -226,7 +182,6 @@ sqfs_block_writer_t *sqfs_block_writer_create(sqfs_file_t *file,
 	((sqfs_block_writer_t *)wr)->get_block_count = get_block_count;
 	wr->flags = flags;
 	wr->file = sqfs_grab(file);
-	wr->devblksz = devblksz;
 
 	if (array_init(&(wr->blocks), sizeof(blk_info_t), INIT_BLOCK_COUNT)) {
 		sqfs_drop(wr->file);