[mtd-utils patch 2/2] Add favourlzo compression mode

[Richard Purdie]

Add a favourlzo compression mode to mtd-utils

This allows lzo compression to be used in the cases where the
compression ratio isn't quite as good zlib. This can make sense in
certain use cases because LZO decompression is much faster than zlib.

Signed-off-by: Richard Purdie <rpurdie at openedhand.com>

---
 compr.c |   52 +++++++++++++++++++++++++++++++++++++++++++++++++---
 compr.h |    1 +
 2 files changed, 50 insertions(+), 3 deletions(-)

Index: git/compr.c
===================================================================
--- git.orig/compr.c	2007-03-01 11:58:01.000000000 +0000
+++ git/compr.c	2007-03-01 11:58:09.000000000 +0000
@@ -16,6 +16,8 @@
 #include <stdlib.h>
 #include <linux/jffs2.h>
 
+#define FAVOUR_LZO_PERCENT 80
+
 extern int page_size;
 
 /* LIST IMPLEMENTATION (from linux/list.h) */
@@ -166,6 +168,33 @@ static void jffs2_decompression_test(str
 	}
 }
 
+/*
+ * Return 1 to use this compression
+ */
+static int jffs2_is_best_compression(struct jffs2_compressor *this,
+		struct jffs2_compressor *best, uint32_t size, uint32_t bestsize)
+{
+	switch (jffs2_compression_mode) {
+		case JFFS2_COMPR_MODE_SIZE:
+			if (bestsize > size)
+				return 1;
+			return 0;
+		case JFFS2_COMPR_MODE_FAVOURLZO:
+			if ((this->compr == JFFS2_COMPR_LZO) && (bestsize > size))
+				return 1;
+			if ((best->compr != JFFS2_COMPR_LZO) && (bestsize > size))
+				return 1;
+			if ((this->compr == JFFS2_COMPR_LZO) && (bestsize > (size * FAVOUR_LZO_PERCENT / 100)))
+				return 1;
+			if ((bestsize * FAVOUR_LZO_PERCENT / 100) > size)
+				return 1;
+
+			return 0;
+	}
+	/* Shouldn't happen */
+	return 0;
+}
+
 /* jffs2_compress:
  * @data: Pointer to uncompressed data
  * @cdata: Pointer to returned pointer to buffer for compressed data
@@ -231,21 +260,29 @@ uint16_t jffs2_compress( unsigned char *
 			}
 			if (ret == JFFS2_COMPR_NONE) free(output_buf);
 			break;
+		case JFFS2_COMPR_MODE_FAVOURLZO:
 		case JFFS2_COMPR_MODE_SIZE:
 			orig_slen = *datalen;
 			orig_dlen = *cdatalen;
 			list_for_each_entry(this, &jffs2_compressor_list, list) {
+				uint32_t needed_buf_size;
+
+				if (jffs2_compression_mode == JFFS2_COMPR_MODE_FAVOURLZO)
+					needed_buf_size = orig_slen+jffs2_compression_check;
+				else
+					needed_buf_size = orig_dlen+jffs2_compression_check;
+
 				/* Skip decompress-only backwards-compatibility and disabled modules */
 				if ((!this->compress)||(this->disabled))
 					continue;
 				/* Allocating memory for output buffer if necessary */
-				if ((this->compr_buf_size<orig_dlen+jffs2_compression_check)&&(this->compr_buf)) {
+				if ((this->compr_buf_size < needed_buf_size) && (this->compr_buf)) {
 					free(this->compr_buf);
 					this->compr_buf_size=0;
 					this->compr_buf=NULL;
 				}
 				if (!this->compr_buf) {
-					tmp_buf = malloc(orig_dlen+jffs2_compression_check);
+					tmp_buf = malloc(needed_buf_size);
 					if (!tmp_buf) {
 						fprintf(stderr,"mkfs.jffs2: No memory for compressor allocation. (%d bytes)\n",orig_dlen);
 						continue;
@@ -265,7 +302,8 @@ uint16_t jffs2_compress( unsigned char *
 				if (!compr_ret) {
 					if (jffs2_compression_check)
 						jffs2_decompression_test(this, data_in, this->compr_buf, *cdatalen, *datalen, this->compr_buf_size);
-					if ((!best_dlen)||(best_dlen>*cdatalen)) {
+					if (((!best_dlen) || jffs2_is_best_compression(this, best, *cdatalen, best_dlen))
+								&& (*cdatalen < *datalen)) {
 						best_dlen = *cdatalen;
 						best_slen = *datalen;
 						best = this;
@@ -377,6 +415,9 @@ char *jffs2_stats(void)
 		case JFFS2_COMPR_MODE_SIZE:
 			act_buf += sprintf(act_buf,"size");
 			break;
+		case JFFS2_COMPR_MODE_FAVOURLZO:
+			act_buf += sprintf(act_buf,"favourlzo");
+			break;
 		default:
 			act_buf += sprintf(act_buf,"unkown");
 			break;
@@ -413,6 +454,11 @@ int jffs2_set_compression_mode_name(cons
 		jffs2_compression_mode = JFFS2_COMPR_MODE_SIZE;
 		return 0;
 	}
+	if (!strcmp("favourlzo", name)) {
+		jffs2_compression_mode = JFFS2_COMPR_MODE_FAVOURLZO;
+		return 0;
+	}
+
 	return 1;
 }
 
Index: git/compr.h
===================================================================
--- git.orig/compr.h	2007-03-01 11:58:01.000000000 +0000
+++ git/compr.h	2007-03-01 11:58:09.000000000 +0000
@@ -32,6 +32,7 @@
 #define JFFS2_COMPR_MODE_NONE       0
 #define JFFS2_COMPR_MODE_PRIORITY   1
 #define JFFS2_COMPR_MODE_SIZE       2
+#define JFFS2_COMPR_MODE_FAVOURLZO  3
 
 #define kmalloc(a,b)                malloc(a)
 #define kfree(a)                    free(a)