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

[Li Guifu via Linux-erofs]

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....@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