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>

7 files changed, 14 insertions, 81 deletions

diff --git a/bin/gensquashfs/src/sort_by_file.c b/bin/gensquashfs/src/sort_by_file.c
index a555718..bc89c39 100644
--- a/bin/gensquashfs/src/sort_by_file.c
+++ b/bin/gensquashfs/src/sort_by_file.c
@@ -159,9 +159,6 @@ static int decode_flags(const char *filename, size_t line_no, bool *do_glob,
 		} else if (strncmp(line, "dont_fragment", 13) == 0) {
 			line += 13;
 			(*flags) |= SQFS_BLK_DONT_FRAGMENT;
-		} else if (strncmp(line, "align", 5) == 0) {
-			line += 5;
-			(*flags) |= SQFS_BLK_ALIGN;
 		} else if (strncmp(line, "dont_compress", 13) == 0) {
 			line += 13;
 			(*flags) |= SQFS_BLK_DONT_COMPRESS;
diff --git a/bin/gensquashfs/test/sort_file.c b/bin/gensquashfs/test/sort_file.c
index 951328e..6c6cce6 100644
--- a/bin/gensquashfs/test/sort_file.c
+++ b/bin/gensquashfs/test/sort_file.c
@@ -42,7 +42,7 @@ static const char *sort_file =
 "  50 [glob] /bin/*\n"
 "\n"
 "# Make this file appear first\n"
-"  -10000 [dont_compress,dont_fragment,align] /usr/share/bla.txt";
+"  -10000 [dont_compress,dont_fragment] /usr/share/bla.txt";
 
 static const char *initial_order[] = {
 	"bin/chmod",
@@ -93,7 +93,7 @@ static sqfs_s64 priorities[] = {
 };
 
 static int flags[] = {
-	SQFS_BLK_DONT_COMPRESS | SQFS_BLK_ALIGN | SQFS_BLK_DONT_FRAGMENT,
+	SQFS_BLK_DONT_COMPRESS | SQFS_BLK_DONT_FRAGMENT,
 	0,
 	0,
 	0,
diff --git a/include/sqfs/block.h b/include/sqfs/block.h
index 30f181c..639fb68 100644
--- a/include/sqfs/block.h
+++ b/include/sqfs/block.h
@@ -72,12 +72,9 @@ typedef enum {
 	SQFS_BLK_DONT_COMPRESS = 0x0001,
 
 	/**
-	 * @brief Align the block on disk to device block size.
-	 *
-	 * If set, the @ref sqfs_block_processor_t will add padding before the
-	 * first block of the affected file and after the last block.
+	 * @brief Don't compute block data checksums.
 	 */
-	SQFS_BLK_ALIGN = 0x0002,
+	SQFS_BLK_DONT_HASH = 0x0002,
 
 	/**
 	 * @brief Don't add the tail end of a file to a fragment block.
@@ -105,11 +102,6 @@ typedef enum {
 	SQFS_BLK_IGNORE_SPARSE = 0x0010,
 
 	/**
-	 * @brief Don't compute block data checksums.
-	 */
-	SQFS_BLK_DONT_HASH = 0x0020,
-
-	/**
 	 * @brief Set by the @ref sqfs_block_processor_t if it determines a
 	 *        block of a file to be sparse, i.e. only zero bytes.
 	 */
@@ -148,9 +140,9 @@ typedef enum {
 	/**
 	 * @brief The combination of all flags that are user settable.
 	 */
-	SQFS_BLK_USER_SETTABLE_FLAGS = 0x003F,
+	SQFS_BLK_USER_SETTABLE_FLAGS = 0x001F,
 
-	SQFS_BLK_FLAGS_ALL = 0xFC3F,
+	SQFS_BLK_FLAGS_ALL = 0xFC1F,
 } SQFS_BLK_FLAGS;
 
 #endif /* SQFS_BLOCK_H */
diff --git a/include/sqfs/block_writer.h b/include/sqfs/block_writer.h
index 6376d2e..84e6973 100644
--- a/include/sqfs/block_writer.h
+++ b/include/sqfs/block_writer.h
@@ -52,11 +52,6 @@ struct sqfs_block_writer_t {
 	 * @ref SQFS_BLK_LAST_BLOCK flag is set, it uses those stored locations
 	 * to do block deduplication.
 	 *
-	 * If the flag @ref SQFS_BLK_ALIGN is set in combination with the
-	 * @ref SQFS_BLK_FIRST_BLOCK, the file size is padded to a multiple of
-	 * the device block size before writing. If it is set together with the
-	 * @ref SQFS_BLK_LAST_BLOCK flag, the padding is added afterwards.
-	 *
 	 * @param wr A pointer to a block writer.
 	 * @param user An optional user data pointer.
 	 *             The @ref sqfs_block_processor_t can be told to pass this
@@ -126,15 +121,12 @@ extern "C" {
  * @memberof sqfs_block_writer_t
  *
  * @param file A pointer to a file object that data should be appended to.
- * @param devblksz The underlying device block size if output data
- *                 should be aligned.
  * @param flags A combination of @ref SQFS_BLOCK_WRITER_FLAGS values. If an
  *              unknown flag is set, creation will fail.
  *
  * @return A pointer to a new block writer on success, NULL on failure.
  */
 SQFS_API sqfs_block_writer_t *sqfs_block_writer_create(sqfs_file_t *file,
-						       size_t devblksz,
 						       sqfs_u32 flags);
 
 #ifdef __cplusplus
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);