This patch has been edited to apply to squashfs 4.4, commit 52eb4c279cd283ed9802dd1ceb686560b22ffb67. Below is the original message body of the patch. From 7bda7c75748f36b0a50f93e46144d5a4de4974ad Mon Sep 17 00:00:00 2001 From: Amin Hassani Date: Thu, 15 Dec 2016 10:43:15 -0800 Subject: [PATCH] mksquashfs 4K aligns the files inside the squashfs image Files inside a squashfs image are not necessarily 4k (4096) aligned. This patch starts each file in a 4k aligned address and pads zero to the end of the file until it reaches the next 4k aligned address. This will not change the size of the compressed blocks (especially the last one) and hence it will not change how the files are being loaded in kernel or unsquashfs. However on average this increases the size of the squashfs image which can be calculated by the following formula: increased_size = (number_of_unfragmented_files_in_image + number of fragments) * 2048 The 4k alignment can be enabled by flag '-4k-align' --- squashfs-tools/mksquashfs.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/squashfs-tools/mksquashfs.c b/squashfs-tools/mksquashfs.c index a45b77f..07b1c06 100644 --- a/squashfs-tools/mksquashfs.c +++ b/squashfs-tools/mksquashfs.c @@ -102,7 +102,9 @@ int old_exclude = TRUE; int use_regex = FALSE; int nopad = FALSE; int exit_on_error = FALSE; +int do_4k_align = FALSE; long long start_offset = 0; +#define ALIGN_UP(bytes, size) (bytes = (bytes + size - 1) & ~(size - 1)) long long global_uid = -1, global_gid = -1; @@ -1546,6 +1548,9 @@ void unlock_fragments() * queue at this time. */ while(!queue_empty(locked_fragment)) { + // 4k align the start of remaining queued fragments. + if(do_4k_align) + ALIGN_UP(bytes, 4096); write_buffer = queue_get(locked_fragment); frg = write_buffer->block; size = SQUASHFS_COMPRESSED_SIZE_BLOCK(fragment_table[frg].size); @@ -2478,6 +2483,9 @@ void *frag_deflator(void *arg) write_buffer->size = compressed_size; pthread_mutex_lock(&fragment_mutex); if(fragments_locked == FALSE) { + // 4k align the start of each fragment. + if(do_4k_align) + ALIGN_UP(bytes, 4096); fragment_table[file_buffer->block].size = c_byte; fragment_table[file_buffer->block].start_block = bytes; write_buffer->block = bytes; @@ -2877,6 +2885,10 @@ int write_file_blocks(squashfs_inode *inode, struct dir_ent *dir_ent, long long sparse = 0; struct file_buffer *fragment_buffer = NULL; + // 4k align the start of each file. + if(do_4k_align) + ALIGN_UP(bytes, 4096); + if(pre_duplicate(read_size)) return write_file_blocks_dup(inode, dir_ent, read_buffer, dup); @@ -4972,6 +4984,7 @@ void write_filesystem_tables(struct squashfs_super_block *sBlk, int nopad) "compressed", no_fragments ? "no" : noF ? "uncompressed" : "compressed", no_xattrs ? "no" : noX ? "uncompressed" : "compressed", noI || noId ? "uncompressed" : "compressed"); + printf("\t4k %saligned\n", do_4k_align ? "" : "un"); printf("\tduplicates are %sremoved\n", duplicate_checking ? "" : "not "); printf("Filesystem size %.2f Kbytes (%.2f Mbytes)\n", bytes / 1024.0, @@ -5853,6 +5866,8 @@ print_compressor_options: root_name = argv[i]; } else if(strcmp(argv[i], "-version") == 0) { VERSION(); + } else if(strcmp(argv[i], "-4k-align") == 0) { + do_4k_align = TRUE; } else { ERROR("%s: invalid option\n\n", argv[0]); printOptions: @@ -5904,6 +5919,7 @@ printOptions: ERROR("\t\t\tdirectory containing that directory, " "rather than the\n"); ERROR("\t\t\tcontents of the directory\n"); + ERROR("-4k-align\t\tenables 4k alignment of all files\n"); ERROR("\nFilesystem filter options:\n"); ERROR("-p \tAdd pseudo file " "definition\n"); -- 2.23.0