erofs: improve decompression error reporting

Change the return type of decompress() from `int` to `const char *` to
provide more informative error diagnostics:

 - A NULL return indicates successful decompression;

 - If IS_ERR(ptr) is true, the return value encodes a standard negative
   errno (e.g., -ENOMEM, -EOPNOTSUPP) identifying the specific error;

 - Otherwise, a non-NULL return points to a human-readable error string,
   and the corresponding error code should be treated as -EFSCORRUPTED.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Author: hsiangkao

fs/erofs/compress.h

@@ -23,8 +23,8 @@ struct z_erofs_decompress_req {
 struct z_erofs_decompressor {
 	int (*config)(struct super_block *sb, struct erofs_super_block *dsb,
 		      void *data, int size);
-	int (*decompress)(struct z_erofs_decompress_req *rq,
-			  struct page **pagepool);
+	const char *(*decompress)(struct z_erofs_decompress_req *rq,
+				  struct page **pagepool);
 	int (*init)(void);
 	void (*exit)(void);
 	char *name;

fs/erofs/decompressor.c

@@ -235,8 +235,6 @@ static int z_erofs_lz4_decompress_mem(struct z_erofs_decompress_req *rq, u8 *dst
 					  rq->inputsize, rq->outputsize);
 
 	if (ret != rq->outputsize) {
-		erofs_err(rq->sb, "failed to decompress %d in[%u, %u] out[%u]",
-			  ret, rq->inputsize, inputmargin, rq->outputsize);
 		if (ret >= 0)
 			memset(out + ret, 0, rq->outputsize - ret);
 		ret = -EFSCORRUPTED;
@@ -257,8 +255,8 @@ static int z_erofs_lz4_decompress_mem(struct z_erofs_decompress_req *rq, u8 *dst
 	return ret;
 }
 
-static int z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq,
-				  struct page **pagepool)
+static const char *z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq,
+					  struct page **pagepool)
 {
 	unsigned int dst_maptype;
 	void *dst;
@@ -273,14 +271,14 @@ static int z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq,
 		/* general decoding path which can be used for all cases */
 		ret = z_erofs_lz4_prepare_dstpages(rq, pagepool);
 		if (ret < 0)
-			return ret;
+			return ERR_PTR(ret);
 		if (ret > 0) {
 			dst = page_address(*rq->out);
 			dst_maptype = 1;
 		} else {
 			dst = erofs_vm_map_ram(rq->out, rq->outpages);
 			if (!dst)
-				return -ENOMEM;
+				return ERR_PTR(-ENOMEM);
 			dst_maptype = 2;
 		}
 	}
@@ -289,19 +287,19 @@ static int z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq,
 		kunmap_local(dst);
 	else if (dst_maptype == 2)
 		vm_unmap_ram(dst, rq->outpages);
-	return ret;
+	return ERR_PTR(ret);
 }
 
-static int z_erofs_transform_plain(struct z_erofs_decompress_req *rq,
-				   struct page **pagepool)
+static const char *z_erofs_transform_plain(struct z_erofs_decompress_req *rq,
+					   struct page **pagepool)
 {
 	const unsigned int nrpages_in = rq->inpages, nrpages_out = rq->outpages;
 	const unsigned int bs = rq->sb->s_blocksize;
 	unsigned int cur = 0, ni = 0, no, pi, po, insz, cnt;
 	u8 *kin;
 
 	if (rq->outputsize > rq->inputsize)
-		return -EOPNOTSUPP;
+		return ERR_PTR(-EOPNOTSUPP);
 	if (rq->alg == Z_EROFS_COMPRESSION_INTERLACED) {
 		cur = bs - (rq->pageofs_out & (bs - 1));
 		pi = (rq->pageofs_in + rq->inputsize - cur) & ~PAGE_MASK;
@@ -341,7 +339,7 @@ static int z_erofs_transform_plain(struct z_erofs_decompress_req *rq,
 		kunmap_local(kin);
 	}
 	DBG_BUGON(ni > nrpages_in);
-	return 0;
+	return NULL;
 }
 
 int z_erofs_stream_switch_bufs(struct z_erofs_stream_dctx *dctx, void **dst,

fs/erofs/decompressor_deflate.c

@@ -157,8 +157,6 @@ static int __z_erofs_deflate_decompress(struct z_erofs_decompress_req *rq,
 				break;
 			if (zerr == Z_STREAM_END && !rq->outputsize)
 				break;
-			erofs_err(sb, "failed to decompress %d in[%u] out[%u]",
-				  zerr, rq->inputsize, rq->outputsize);
 			err = -EFSCORRUPTED;
 			break;
 		}
@@ -178,20 +176,20 @@ static int __z_erofs_deflate_decompress(struct z_erofs_decompress_req *rq,
 	return err;
 }
 
-static int z_erofs_deflate_decompress(struct z_erofs_decompress_req *rq,
-				      struct page **pgpl)
+static const char *z_erofs_deflate_decompress(struct z_erofs_decompress_req *rq,
+					      struct page **pgpl)
 {
 #ifdef CONFIG_EROFS_FS_ZIP_ACCEL
 	int err;
 
 	if (!rq->partial_decoding) {
 		err = z_erofs_crypto_decompress(rq, pgpl);
 		if (err != -EOPNOTSUPP)
-			return err;
+			return ERR_PTR(err);
 
 	}
 #endif
-	return __z_erofs_deflate_decompress(rq, pgpl);
+	return ERR_PTR(__z_erofs_deflate_decompress(rq, pgpl));
 }
 
 const struct z_erofs_decompressor z_erofs_deflate_decomp = {

fs/erofs/decompressor_lzma.c

@@ -146,8 +146,8 @@ static int z_erofs_load_lzma_config(struct super_block *sb,
 	return err;
 }
 
-static int z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
-				   struct page **pgpl)
+static const char *z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
+					   struct page **pgpl)
 {
 	struct super_block *sb = rq->sb;
 	struct z_erofs_stream_dctx dctx = { .rq = rq, .no = -1, .ni = 0 };
@@ -162,7 +162,7 @@ static int z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
 			min(rq->inputsize, sb->s_blocksize - rq->pageofs_in));
 	if (err) {
 		kunmap_local(dctx.kin);
-		return err;
+		return ERR_PTR(err);
 	}
 
 	/* 2. get an available lzma context */
@@ -207,8 +207,6 @@ static int z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
 		if (xz_err != XZ_OK) {
 			if (xz_err == XZ_STREAM_END && !rq->outputsize)
 				break;
-			erofs_err(sb, "failed to decompress %d in[%u] out[%u]",
-				  xz_err, rq->inputsize, rq->outputsize);
 			err = -EFSCORRUPTED;
 			break;
 		}
@@ -223,7 +221,7 @@ static int z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
 	z_erofs_lzma_head = strm;
 	spin_unlock(&z_erofs_lzma_lock);
 	wake_up(&z_erofs_lzma_wq);
-	return err;
+	return ERR_PTR(err);
 }
 
 const struct z_erofs_decompressor z_erofs_lzma_decomp = {

fs/erofs/decompressor_zstd.c

@@ -135,8 +135,8 @@ static int z_erofs_load_zstd_config(struct super_block *sb,
 	return strm ? -ENOMEM : 0;
 }
 
-static int z_erofs_zstd_decompress(struct z_erofs_decompress_req *rq,
-				   struct page **pgpl)
+static const char *z_erofs_zstd_decompress(struct z_erofs_decompress_req *rq,
+					   struct page **pgpl)
 {
 	struct super_block *sb = rq->sb;
 	struct z_erofs_stream_dctx dctx = { .rq = rq, .no = -1, .ni = 0 };
@@ -152,7 +152,7 @@ static int z_erofs_zstd_decompress(struct z_erofs_decompress_req *rq,
 			min(rq->inputsize, sb->s_blocksize - rq->pageofs_in));
 	if (err) {
 		kunmap_local(dctx.kin);
-		return err;
+		return ERR_PTR(err);
 	}
 
 	/* 2. get an available ZSTD context */
@@ -191,10 +191,6 @@ static int z_erofs_zstd_decompress(struct z_erofs_decompress_req *rq,
 		if (zstd_is_error(zerr) ||
 		    ((rq->outputsize + dctx.avail_out) && (!zerr || (zerr > 0 &&
 				!(rq->inputsize + in_buf.size - in_buf.pos))))) {
-			erofs_err(sb, "failed to decompress in[%u] out[%u]: %s",
-				  rq->inputsize, rq->outputsize,
-				  zstd_is_error(zerr) ? zstd_get_error_name(zerr) :
-					"unexpected end of stream");
 			err = -EFSCORRUPTED;
 			break;
 		}
@@ -210,7 +206,7 @@ static int z_erofs_zstd_decompress(struct z_erofs_decompress_req *rq,
 	z_erofs_zstd_head = strm;
 	spin_unlock(&z_erofs_zstd_lock);
 	wake_up(&z_erofs_zstd_wq);
-	return err;
+	return ERR_PTR(err);
 }
 
 const struct z_erofs_decompressor z_erofs_zstd_decomp = {

fs/erofs/zdata.c

@@ -1267,12 +1267,13 @@ static int z_erofs_decompress_pcluster(struct z_erofs_backend *be, int err)
 	struct erofs_sb_info *const sbi = EROFS_SB(be->sb);
 	struct z_erofs_pcluster *pcl = be->pcl;
 	unsigned int pclusterpages = z_erofs_pclusterpages(pcl);
-	const struct z_erofs_decompressor *decomp =
+	const struct z_erofs_decompressor *alg =
 				z_erofs_decomp[pcl->algorithmformat];
+	bool try_free = true;
 	int i, j, jtop, err2;
 	struct page *page;
 	bool overlapped;
-	bool try_free = true;
+	const char *reason;
 
 	mutex_lock(&pcl->lock);
 	be->nr_pages = PAGE_ALIGN(pcl->length + pcl->pageofs_out) >> PAGE_SHIFT;
@@ -1304,8 +1305,8 @@ static int z_erofs_decompress_pcluster(struct z_erofs_backend *be, int err)
 	err2 = z_erofs_parse_in_bvecs(be, &overlapped);
 	if (err2)
 		err = err2;
-	if (!err)
-		err = decomp->decompress(&(struct z_erofs_decompress_req) {
+	if (!err) {
+		reason = alg->decompress(&(struct z_erofs_decompress_req) {
 					.sb = be->sb,
 					.in = be->compressed_pages,
 					.out = be->decompressed_pages,
@@ -1322,6 +1323,18 @@ static int z_erofs_decompress_pcluster(struct z_erofs_backend *be, int err)
 					.gfp = pcl->besteffort ? GFP_KERNEL :
 						GFP_NOWAIT | __GFP_NORETRY
 				 }, be->pagepool);
+		if (IS_ERR(reason)) {
+			erofs_err(be->sb, "failed to decompress (%s) %ld @ pa %llu size %u => %u",
+				  alg->name, PTR_ERR(reason), pcl->pos,
+				  pcl->pclustersize, pcl->length);
+			err = PTR_ERR(reason);
+		} else if (unlikely(reason)) {
+			erofs_err(be->sb, "failed to decompress (%s) %s @ pa %llu size %u => %u",
+				  alg->name, reason, pcl->pos,
+				  pcl->pclustersize, pcl->length);
+			err = -EFSCORRUPTED;
+		}
+	}
 
 	/* must handle all compressed pages before actual file pages */
 	if (pcl->from_meta) {