erofs: improve LZ4 error strings

Just like what was done for other algorithms, let's propagate detailed
error reasons for LZ4 instead of just -EFSCORRUPTED to users:

 "corrupted compressed data":
    the compressed data is malformed or
      destination buffer is not large enough

 "unexpected end of stream":
    the compressed stream ends normally, but without producing enough
    decompressed data.

 "compressed data start not found":
    can be returned by z_erofs_fixup_insize().

Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
index 15b464a589939d46769d405774e554931612740b..e9d799a03a91f4a3429063d55bf0ba1d2e47ac14 100644 (file)
--- a/fs/erofs/decompressor.c
+++ b/fs/erofs/decompressor.c
@@ -195,26 +195,25 @@ const char *z_erofs_fixup_insize(struct z_erofs_decompress_req *rq,
        return NULL;
 }
 
-static int z_erofs_lz4_decompress_mem(struct z_erofs_decompress_req *rq, u8 *dst)
+static const char *__z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq,
+                                           u8 *dst)
 {
-       bool support_0padding = false, may_inplace = false;
+       bool zeropadded = erofs_sb_has_zero_padding(EROFS_SB(rq->sb));
+       bool may_inplace = false;
        unsigned int inputmargin;
        u8 *out, *headpage, *src;
        const char *reason;
        int ret, maptype;
 
-       DBG_BUGON(*rq->in == NULL);
        headpage = kmap_local_page(*rq->in);
-
        /* LZ4 decompression inplace is only safe if zero_padding is enabled */
-       if (erofs_sb_has_zero_padding(EROFS_SB(rq->sb))) {
-               support_0padding = true;
+       if (zeropadded) {
                reason = z_erofs_fixup_insize(rq, headpage + rq->pageofs_in,
                                min_t(unsigned int, rq->inputsize,
                                      rq->sb->s_blocksize - rq->pageofs_in));
                if (reason) {
                        kunmap_local(headpage);
-                       return IS_ERR(reason) ? PTR_ERR(reason) : -EFSCORRUPTED;
+                       return reason;
                }
                may_inplace = !((rq->pageofs_in + rq->inputsize) &
                                (rq->sb->s_blocksize - 1));
@@ -224,26 +223,24 @@ static int z_erofs_lz4_decompress_mem(struct z_erofs_decompress_req *rq, u8 *dst
        src = z_erofs_lz4_handle_overlap(rq, headpage, dst, &inputmargin,
                                         &maptype, may_inplace);
        if (IS_ERR(src))
-               return PTR_ERR(src);
+               return ERR_CAST(src);
 
        out = dst + rq->pageofs_out;
        /* legacy format could compress extra data in a pcluster. */
-       if (rq->partial_decoding || !support_0padding)
+       if (rq->partial_decoding || !zeropadded)
                ret = LZ4_decompress_safe_partial(src + inputmargin, out,
                                rq->inputsize, rq->outputsize, rq->outputsize);
        else
                ret = LZ4_decompress_safe(src + inputmargin, out,
                                          rq->inputsize, rq->outputsize);
+       if (ret == rq->outputsize)
+               reason = NULL;
+       else if (ret < 0)
+               reason = "corrupted compressed data";
+       else
+               reason = "unexpected end of stream";
 
-       if (ret != rq->outputsize) {
-               if (ret >= 0)
-                       memset(out + ret, 0, rq->outputsize - ret);
-               ret = -EFSCORRUPTED;
-       } else {
-               ret = 0;
-       }
-
-       if (maptype == 0) {
+       if (!maptype) {
                kunmap_local(headpage);
        } else if (maptype == 1) {
                vm_unmap_ram(src, rq->inpages);
@@ -251,15 +248,16 @@ static int z_erofs_lz4_decompress_mem(struct z_erofs_decompress_req *rq, u8 *dst
                z_erofs_put_gbuf(src);
        } else if (maptype != 3) {
                DBG_BUGON(1);
-               return -EFAULT;
+               return ERR_PTR(-EFAULT);
        }
-       return ret;
+       return reason;
 }
 
 static const char *z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq,
                                          struct page **pagepool)
 {
        unsigned int dst_maptype;
+       const char *reason;
        void *dst;
        int ret;
 
@@ -283,12 +281,12 @@ static const char *z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq,
                        dst_maptype = 2;
                }
        }
-       ret = z_erofs_lz4_decompress_mem(rq, dst);
+       reason = __z_erofs_lz4_decompress(rq, dst);
        if (!dst_maptype)
                kunmap_local(dst);
        else if (dst_maptype == 2)
                vm_unmap_ram(dst, rq->outpages);
-       return ERR_PTR(ret);
+       return reason;
 }
 
 static const char *z_erofs_transform_plain(struct z_erofs_decompress_req *rq,