Yifan Zhao <[email protected]> 于2026年7月9日周四 20:36写道：
>
> With ztailpacking, the final compressed pcluster is first stored as
> inline data. If the inode metadata area cannot hold it, mkfs falls back
> to a normal tail block and drops the inline pcluster marker.
>
> The current fallback path assumes that the inline tail pcluster belongs
> to the EOF lcluster. That is not always true: the tail pcluster can
> start in the previous lcluster and end at EOF, while its raw size still
> fits in one block. In that case, patching the EOF lcluster is
> semantically wrong.
>
> Let's keep raw tail data whenever it fits in one block, and convert the
> corresponding lcluster index to PLAIN during fallback.
>
> Reported-by: Alberto Salvia Novella <[email protected]>
> Closes: https://github.com/erofs/erofs-utils/issues/51
> Assisted-by: Codex:GPT-5.5
> Signed-off-by: Yifan Zhao <[email protected]>
> ---
Hi Yifan,
I tested this patch to focus on the issue fixed by commit
277a42502a7a, and it passed.
But I have some questions:
> include/erofs/internal.h | 5 +-
> lib/compress.c | 109 ++++++++++++++++++++++++++++-----------
> 2 files changed, 83 insertions(+), 31 deletions(-)
>
> diff --git a/include/erofs/internal.h b/include/erofs/internal.h
> index 2cc9cc8..bdde41f 100644
> --- a/include/erofs/internal.h
> +++ b/include/erofs/internal.h
> @@ -212,8 +212,11 @@ struct erofs_diskbuf;
>
> enum erofs_idata_type {
> EROFS_IDATA_TYPE_RAW,
> - EROFS_IDATA_TYPE_COMPRESSED_DEFAULT,
> + EROFS_IDATA_TYPE_COMPRESSED,
> + /* compressed idata follows a final 2B compacted index pack */
> EROFS_IDATA_TYPE_COMPRESSED_END_OF_2B,
> + /* compressed idata follows a final single-entry 4B pack after a 2B
> pack */
> + EROFS_IDATA_TYPE_COMPRESSED_4B1_PREV2B,
> };
>
> #define EROFS_I_BLKADDR_DEV_ID_BIT 48
> diff --git a/lib/compress.c b/lib/compress.c
> index f7ad5a1..ec90f65 100644
> --- a/lib/compress.c
> +++ b/lib/compress.c
> @@ -483,7 +483,7 @@ static int z_erofs_fill_inline_data(struct erofs_inode
> *inode, void *data,
> {
> inode->z_advise |= Z_EROFS_ADVISE_INLINE_PCLUSTER;
> inode->idata_size = len;
> - inode->idata_type = EROFS_IDATA_TYPE_COMPRESSED_DEFAULT;
> + inode->idata_type = EROFS_IDATA_TYPE_COMPRESSED;
>
> inode->idata = malloc(inode->idata_size);
> if (!inode->idata)
> @@ -664,7 +664,7 @@ frag_packing:
> ictx->fragemitted = true;
> /* tailpcluster should be less than 1 block */
> } else if (may_inline && len == e->length && compressedsize < blksz) {
> - if (ctx->clusterofs + len <= blksz) {
Shouldn't this condition restrict the `tail pcluster` so that it
corresponds to only eof`lcluster`?
and we drop the inline pcluster just when eof_tailraw is not null.
Thanks!
> + if (len <= blksz) {
> inode->eof_tailraw = malloc(len);
> if (!inode->eof_tailraw)
> return -ENOMEM;
> @@ -962,6 +962,14 @@ int z_erofs_convert_to_compacted_format(struct
> erofs_inode *inode,
> dummy_head = true;
> }
>
> + if (inode->idata_size) {
> + if (compacted_2b && !compacted_4b_end)
> + inode->idata_type =
> EROFS_IDATA_TYPE_COMPRESSED_END_OF_2B;
> + else if (compacted_2b && compacted_4b_end == 1)
> + inode->idata_type =
> + EROFS_IDATA_TYPE_COMPRESSED_4B1_PREV2B;
> + }
> +
> /* generate compacted_4b_initial */
> while (compacted_4b_initial) {
> in = parse_legacy_indexes(cv, 2, in);
> @@ -974,8 +982,6 @@ int z_erofs_convert_to_compacted_format(struct
> erofs_inode *inode,
>
> /* generate compacted_2b */
> if (compacted_2b) {
> - if (!compacted_4b_end && inode->idata_size)
> - inode->idata_type =
> EROFS_IDATA_TYPE_COMPRESSED_END_OF_2B;
> do {
> in = parse_legacy_indexes(cv, 16, in);
> out = write_compacted_indexes(out, cv, &blkaddr,
> @@ -1205,11 +1211,65 @@ out:
> return metabuf;
> }
>
> +static void z_erofs_patch_tail_compacted_index(struct erofs_inode *inode,
> + bool previous,
> + unsigned int type)
> +{
> + const unsigned int totalidx = BLK_ROUND_UP(inode->sbi, inode->i_size);
> + const unsigned int lobits = max_t(unsigned int, inode->z_lclusterbits,
> + ilog2(Z_EROFS_LI_D0_CBLKCNT) + 1U);
> + u8 *base = inode->compressmeta;
> + u8 *pack = base + inode->extent_isize;
> + unsigned int bitpos, bitoff;
> + u8 *out;
> + u32 v;
> +
> + DBG_BUGON(!totalidx);
> + DBG_BUGON(inode->z_lclusterbits > 14);
> +
> + if (inode->idata_type == EROFS_IDATA_TYPE_COMPRESSED_END_OF_2B) {
> + pack -= 32;
> + bitpos = 14 * (previous ? 14 : 15);
> + goto out;
> + }
> +
> + /* Last compacted index pack is 4B */
> + pack -= 8;
> + if (!(totalidx & 1)) {
> + bitpos = previous ? 0 : 16;
> + goto out;
> + }
> +
> + if (!previous) {
> + bitpos = 0;
> + goto out;
> + }
> +
> + /* Second to last compacted index pack is 2B */
> + if (inode->idata_type == EROFS_IDATA_TYPE_COMPRESSED_4B1_PREV2B) {
> + pack -= 32;
> + bitpos = 14 * 15;
> + } else {
> + pack -= 8;
> + bitpos = 16;
> + }
> +out:
> + DBG_BUGON(pack < base);
> + bitoff = bitpos & 7;
> + out = pack + bitpos / 8;
> + v = get_unaligned_le32(out);
> + v &= ~(Z_EROFS_LI_LCLUSTER_TYPE_MASK << (lobits + bitoff));
> + v |= type << (lobits + bitoff);
> + put_unaligned_le32(v, out);
> +}
> +
> void z_erofs_drop_inline_pcluster(struct erofs_inode *inode)
> {
> struct erofs_sb_info *sbi = inode->sbi;
> const unsigned int type = Z_EROFS_LCLUSTER_TYPE_PLAIN;
> struct z_erofs_map_header *h = inode->compressmeta;
> + erofs_off_t rawstart;
> + erofs_blk_t head_lcn, eof_lcn;
>
> h->h_advise = cpu_to_le16(le16_to_cpu(h->h_advise) &
> ~Z_EROFS_ADVISE_INLINE_PCLUSTER);
> @@ -1218,38 +1278,27 @@ void z_erofs_drop_inline_pcluster(struct erofs_inode
> *inode)
> if (!inode->eof_tailraw)
> return;
> DBG_BUGON(inode->idata_type == EROFS_IDATA_TYPE_RAW);
> + DBG_BUGON(!inode->i_size);
> + DBG_BUGON(inode->eof_tailrawsize > erofs_blksiz(sbi));
> + DBG_BUGON(inode->eof_tailrawsize > inode->i_size);
> +
> + rawstart = inode->i_size - inode->eof_tailrawsize;
> + head_lcn = rawstart >> sbi->blkszbits;
> + eof_lcn = (inode->i_size - 1) >> sbi->blkszbits;
> + DBG_BUGON(head_lcn != eof_lcn && head_lcn + 1 != eof_lcn);
>
> - /* patch the EOF lcluster to uncompressed type first */
> + /* patch the tail pcluster head to uncompressed type first */
> if (inode->datalayout == EROFS_INODE_COMPRESSED_FULL) {
> struct z_erofs_lcluster_index *di =
> - (inode->compressmeta + inode->extent_isize) -
> - sizeof(struct z_erofs_lcluster_index);
> + (void *)((u8 *)inode->compressmeta +
> + Z_EROFS_LEGACY_MAP_HEADER_SIZE +
> + head_lcn *
> + sizeof(struct z_erofs_lcluster_index));
>
> di->di_advise = cpu_to_le16(type);
> } else if (inode->datalayout == EROFS_INODE_COMPRESSED_COMPACT) {
> - /* handle the last compacted 4B/2B pack */
> - unsigned int lclusterbits = inode->z_lclusterbits;
> - unsigned int lobits, eofs, base, pos, v;
> - u8 *out;
> -
> - lobits = max(lclusterbits, ilog2(Z_EROFS_LI_D0_CBLKCNT) + 1U);
> -
> - if (inode->idata_type == EROFS_IDATA_TYPE_COMPRESSED_DEFAULT)
> {
> - eofs = inode->extent_isize -
> - (4 << (BLK_ROUND_UP(sbi, inode->i_size) & 1));
> - base = round_down(eofs, 8);
> - pos = 16 /* encodebits */ * ((eofs - base) / 4);
> - out = inode->compressmeta + base + pos / 8;
> - } else {
> - out = inode->compressmeta + inode->extent_isize -
> - sizeof(__le32) - sizeof(__le16);
> - lobits = 16 - 14 /* encodebits */ + lobits;
> - }
> -
> - v = (get_unaligned_le16(out) & (BIT(lobits) - 1)) |
> - (type << lobits);
> - *out = v & 0xff;
> - *(out + 1) = v >> 8;
> + z_erofs_patch_tail_compacted_index(inode, head_lcn != eof_lcn,
> + type);
> } else {
> DBG_BUGON(1);
> return;
> --
> 2.47.3
>
>
