erofs: don't round offset down for erofs_read_metabuf()

There's only one place where struct z_erofs_maprecorder ->kaddr is
used not in the same function that has assigned it -
the value read in unpack_compacted_index() gets calculated in
z_erofs_load_compact_lcluster().  With minor massage we can switch
to storing it with offset in block already added.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Link: https://lore.kernel.org/r/20240425195944.GE1031757@ZenIV
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
index 8979def17b582cbbab3a521d86ddce417238e5e2..9b248ee5fef2d26e0fae60d67e0c4318d8a1f0bd 100644 (file)
--- a/fs/erofs/zmap.c
+++ b/fs/erofs/zmap.c
@@ -34,13 +34,13 @@ static int z_erofs_load_full_lcluster(struct z_erofs_maprecorder *m,
        unsigned int advise;
 
        m->kaddr = erofs_read_metabuf(&m->map->buf, inode->i_sb,
-                                     erofs_pos(inode->i_sb, erofs_blknr(inode->i_sb, pos)), EROFS_KMAP);
+                                     pos, EROFS_KMAP);
        if (IS_ERR(m->kaddr))
                return PTR_ERR(m->kaddr);
 
        m->nextpackoff = pos + sizeof(struct z_erofs_lcluster_index);
        m->lcn = lcn;
-       di = m->kaddr + erofs_blkoff(inode->i_sb, pos);
+       di = m->kaddr;
 
        advise = le16_to_cpu(di->di_advise);
        m->type = advise & Z_EROFS_LI_LCLUSTER_TYPE_MASK;
@@ -109,7 +109,7 @@ static int unpack_compacted_index(struct z_erofs_maprecorder *m,
 {
        struct erofs_inode *const vi = EROFS_I(m->inode);
        const unsigned int lclusterbits = vi->z_logical_clusterbits;
-       unsigned int vcnt, base, lo, lobits, encodebits, nblk, eofs;
+       unsigned int vcnt, lo, lobits, encodebits, nblk, bytes;
        int i;
        u8 *in, type;
        bool big_pcluster;
@@ -127,11 +127,11 @@ static int unpack_compacted_index(struct z_erofs_maprecorder *m,
        big_pcluster = vi->z_advise & Z_EROFS_ADVISE_BIG_PCLUSTER_1;
        lobits = max(lclusterbits, ilog2(Z_EROFS_LI_D0_CBLKCNT) + 1U);
        encodebits = ((vcnt << amortizedshift) - sizeof(__le32)) * 8 / vcnt;
-       eofs = erofs_blkoff(m->inode->i_sb, pos);
-       base = round_down(eofs, vcnt << amortizedshift);
-       in = m->kaddr + base;
+       bytes = pos & ((vcnt << amortizedshift) - 1);
 
-       i = (eofs - base) >> amortizedshift;
+       in = m->kaddr - bytes;
+
+       i = bytes >> amortizedshift;
 
        lo = decode_compactedbits(lobits, in, encodebits * i, &type);
        m->type = type;
@@ -256,7 +256,7 @@ static int z_erofs_load_compact_lcluster(struct z_erofs_maprecorder *m,
 out:
        pos += lcn * (1 << amortizedshift);
        m->kaddr = erofs_read_metabuf(&m->map->buf, inode->i_sb,
-                                     erofs_pos(inode->i_sb, erofs_blknr(inode->i_sb, pos)), EROFS_KMAP);
+                                     pos, EROFS_KMAP);
        if (IS_ERR(m->kaddr))
                return PTR_ERR(m->kaddr);
        return unpack_compacted_index(m, amortizedshift, pos, lookahead);