[PATCH v2] erofs-utils: add a compress limit to source input stream

[Li Guifu]

It cause a differential amplification when create binary diff
image for upgrade. Give a limits to cut compress, so the amplification
will be limit in the given size.

Signed-off-by: Li Guifu <bluce.lee at aliyun.com>
---
changes since v1:
 - fix variable "readcount" use the min data with comprlimits

 include/erofs/internal.h |  1 +
 lib/compress.c           | 22 +++++++++++++++++-----
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/include/erofs/internal.h b/include/erofs/internal.h
index 41da189..367c0b0 100644
--- a/include/erofs/internal.h
+++ b/include/erofs/internal.h
@@ -41,6 +41,7 @@ typedef unsigned short umode_t;
 
 #define EROFS_ISLOTBITS		5
 #define EROFS_SLOTSIZE		(1U << EROFS_ISLOTBITS)
+#define EROFS_COMPR_LIMITS	(1024U * EROFS_BLKSIZ)
 
 typedef u64 erofs_off_t;
 typedef u64 erofs_nid_t;
diff --git a/lib/compress.c b/lib/compress.c
index 6cc68ed..fe1cb09 100644
--- a/lib/compress.c
+++ b/lib/compress.c
@@ -150,7 +150,7 @@ static int vle_compress_one(struct erofs_inode *inode,
 {
 	struct erofs_compress *const h = &compresshandle;
 	unsigned int len = ctx->tail - ctx->head;
-	unsigned int count;
+	unsigned int count = 0;
 	int ret;
 	static char dstbuf[EROFS_BLKSIZ * 2];
 	char *const dst = dstbuf + EROFS_BLKSIZ;
@@ -159,7 +159,7 @@ static int vle_compress_one(struct erofs_inode *inode,
 		bool raw;
 
 		if (len <= EROFS_BLKSIZ) {
-			if (final)
+			if (!count || final)
 				goto nocompression;
 			break;
 		}
@@ -392,7 +392,7 @@ int erofs_write_compressed_file(struct erofs_inode *inode)
 {
 	struct erofs_buffer_head *bh;
 	struct z_erofs_vle_compress_ctx ctx;
-	erofs_off_t remaining;
+	erofs_off_t remaining, comprlimits;
 	erofs_blk_t blkaddr, compressed_blocks;
 	unsigned int legacymetasize;
 	int ret, fd;
@@ -422,10 +422,14 @@ int erofs_write_compressed_file(struct erofs_inode *inode)
 	ctx.head = ctx.tail = 0;
 	ctx.clusterofs = 0;
 	remaining = inode->i_size;
+	comprlimits = EROFS_COMPR_LIMITS;
 
 	while (remaining) {
-		const u64 readcount = min_t(u64, remaining,
-					    sizeof(ctx.queue) - ctx.tail);
+		const u64 readcount = min_t(u64,
+					     min_t(u64, remaining,
+						sizeof(ctx.queue) - ctx.tail),
+						comprlimits);
+
 
 		ret = read(fd, ctx.queue + ctx.tail, readcount);
 		if (ret != readcount) {
@@ -434,11 +438,19 @@ int erofs_write_compressed_file(struct erofs_inode *inode)
 		}
 		remaining -= readcount;
 		ctx.tail += readcount;
+		comprlimits -= readcount;
 
+compr_continue:
 		/* do one compress round */
 		ret = vle_compress_one(inode, &ctx, false);
 		if (ret)
 			goto err_bdrop;
+		if (!comprlimits) {
+			if (ctx.head != ctx.tail)
+				goto compr_continue;
+			ctx.clusterofs = 0;
+			comprlimits = EROFS_COMPR_LIMITS;
+		}
 	}
 
 	/* do the final round */
-- 
2.17.1