[PATCH] erofs-utils: fix multi-threaded compression in tarerofs mode

[Gao Xiang]

Since pread() can be used during multi-threaded compression, it's
necessary to pass `fpos` in to indicate the absolute offset.

Fixes: aec8487dce4c ("erofs-utils: mkfs: introduce inner-file multi-threaded compression")
Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>
---
 include/erofs/compress.h |  2 +-
 lib/compress.c           | 14 +++++++++-----
 lib/inode.c              |  4 ++--
 3 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/include/erofs/compress.h b/include/erofs/compress.h
index 3253611..871db54 100644
--- a/include/erofs/compress.h
+++ b/include/erofs/compress.h
@@ -18,7 +18,7 @@ extern "C"
 #define Z_EROFS_COMPR_QUEUE_SZ		(EROFS_CONFIG_COMPR_MAX_SZ * 2)
 
 void z_erofs_drop_inline_pcluster(struct erofs_inode *inode);
-int erofs_write_compressed_file(struct erofs_inode *inode, int fd);
+int erofs_write_compressed_file(struct erofs_inode *inode, int fd, u64 fpos);
 
 int z_erofs_compress_init(struct erofs_sb_info *sbi,
 			  struct erofs_buffer_head *bh);
diff --git a/lib/compress.c b/lib/compress.c
index 8d88dd1..e064293 100644
--- a/lib/compress.c
+++ b/lib/compress.c
@@ -38,8 +38,9 @@ struct z_erofs_extent_item {
 
 struct z_erofs_compress_ictx {		/* inode context */
 	struct erofs_inode *inode;
-	int fd;
 	unsigned int pclustersize;
+	int fd;
+	u64 fpos;
 
 	u32 tof_chksum;
 	bool fix_dedupedfrag;
@@ -990,7 +991,8 @@ void z_erofs_drop_inline_pcluster(struct erofs_inode *inode)
 int z_erofs_compress_segment(struct z_erofs_compress_sctx *ctx,
 			     u64 offset, erofs_blk_t blkaddr)
 {
-	int fd = ctx->ictx->fd;
+	struct z_erofs_compress_ictx *ictx = ctx->ictx;
+	int fd = ictx->fd;
 
 	ctx->blkaddr = blkaddr;
 	while (ctx->remaining) {
@@ -1000,7 +1002,8 @@ int z_erofs_compress_segment(struct z_erofs_compress_sctx *ctx,
 
 		ret = (offset == -1 ?
 			read(fd, ctx->queue + ctx->tail, rx) :
-			pread(fd, ctx->queue + ctx->tail, rx, offset));
+			pread(fd, ctx->queue + ctx->tail, rx,
+			      ictx->fpos + offset));
 		if (ret != rx)
 			return -errno;
 
@@ -1238,7 +1241,7 @@ int z_erofs_mt_compress(struct z_erofs_compress_ictx *ictx,
 }
 #endif
 
-int erofs_write_compressed_file(struct erofs_inode *inode, int fd)
+int erofs_write_compressed_file(struct erofs_inode *inode, int fd, u64 fpos)
 {
 	static u8 g_queue[Z_EROFS_COMPR_QUEUE_SZ];
 	struct erofs_buffer_head *bh;
@@ -1313,9 +1316,10 @@ int erofs_write_compressed_file(struct erofs_inode *inode, int fd)
 	blkaddr = erofs_mapbh(bh->block);	/* start_blkaddr */
 	ctx.inode = inode;
 	ctx.pclustersize = z_erofs_get_max_pclustersize(inode);
+	ctx.fd = fd;
+	ctx.fpos = fpos;
 	ctx.metacur = compressmeta + Z_EROFS_LEGACY_MAP_HEADER_SIZE;
 	init_list_head(&ctx.extents);
-	ctx.fd = fd;
 	ctx.fix_dedupedfrag = false;
 	ctx.fragemitted = false;
 	sctx = (struct z_erofs_compress_sctx) { .ictx = &ctx, };
diff --git a/lib/inode.c b/lib/inode.c
index ac00228..4c29aa7 100644
--- a/lib/inode.c
+++ b/lib/inode.c
@@ -493,7 +493,7 @@ int erofs_write_file(struct erofs_inode *inode, int fd, u64 fpos)
 	}
 
 	if (cfg.c_compr_opts[0].alg && erofs_file_is_compressible(inode)) {
-		ret = erofs_write_compressed_file(inode, fd);
+		ret = erofs_write_compressed_file(inode, fd, fpos);
 		if (!ret || ret != -ENOSPC)
 			return ret;
 
@@ -1340,7 +1340,7 @@ struct erofs_inode *erofs_mkfs_build_special_from_fd(int fd, const char *name)
 		inode->nid = inode->sbi->packed_nid;
 	}
 
-	ret = erofs_write_compressed_file(inode, fd);
+	ret = erofs_write_compressed_file(inode, fd, 0);
 	if (ret == -ENOSPC) {
 		ret = lseek(fd, 0, SEEK_SET);
 		if (ret < 0)
-- 
2.39.3