erofs: fix large fragment handling

Fragments aren't limited by Z_EROFS_PCLUSTER_MAX_DSIZE. However, if
a fragment's logical length is larger than Z_EROFS_PCLUSTER_MAX_DSIZE
but the fragment is not the whole inode, it currently returns
-EOPNOTSUPP because m_flags has the wrong EROFS_MAP_ENCODED flag set.
It is not intended by design but should be rare, as it can only be
reproduced by mkfs with `-Eall-fragments` in a specific case.

Let's normalize fragment m_flags using the new EROFS_MAP_FRAGMENT.

Reported-by: Axel Fontaine <axel@axelfontaine.com>
Closes: erofs/erofs-utils#23
Fixes: 7c3ca18 ("erofs: restrict pcluster size limitations")
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20250711195826.3601157-1-hsiangkao@linux.alibaba.com

Author: hsiangkao

fs/erofs/internal.h

@@ -315,10 +315,12 @@ static inline struct folio *erofs_grab_folio_nowait(struct address_space *as,
 /* The length of extent is full */
 #define EROFS_MAP_FULL_MAPPED	0x0008
 /* Located in the special packed inode */
-#define EROFS_MAP_FRAGMENT	0x0010
+#define __EROFS_MAP_FRAGMENT	0x0010
 /* The extent refers to partial decompressed data */
 #define EROFS_MAP_PARTIAL_REF	0x0020
 
+#define EROFS_MAP_FRAGMENT	(EROFS_MAP_MAPPED | __EROFS_MAP_FRAGMENT)
+
 struct erofs_map_blocks {
 	struct erofs_buf buf;
 

fs/erofs/zdata.c

@@ -1034,7 +1034,7 @@ static int z_erofs_scan_folio(struct z_erofs_frontend *f,
 		if (!(map->m_flags & EROFS_MAP_MAPPED)) {
 			folio_zero_segment(folio, cur, end);
 			tight = false;
-		} else if (map->m_flags & EROFS_MAP_FRAGMENT) {
+		} else if (map->m_flags & __EROFS_MAP_FRAGMENT) {
 			erofs_off_t fpos = offset + cur - map->m_la;
 
 			err = z_erofs_read_fragment(inode->i_sb, folio, cur,

fs/erofs/zmap.c

@@ -413,8 +413,7 @@ static int z_erofs_map_blocks_fo(struct inode *inode,
 	    !vi->z_tailextent_headlcn) {
 		map->m_la = 0;
 		map->m_llen = inode->i_size;
-		map->m_flags = EROFS_MAP_MAPPED |
-			EROFS_MAP_FULL_MAPPED | EROFS_MAP_FRAGMENT;
+		map->m_flags = EROFS_MAP_FRAGMENT;
 		return 0;
 	}
 	initial_lcn = ofs >> lclusterbits;
@@ -489,7 +488,7 @@ static int z_erofs_map_blocks_fo(struct inode *inode,
 			goto unmap_out;
 		}
 	} else if (fragment && m.lcn == vi->z_tailextent_headlcn) {
-		map->m_flags |= EROFS_MAP_FRAGMENT;
+		map->m_flags = EROFS_MAP_FRAGMENT;
 	} else {
 		map->m_pa = erofs_pos(sb, m.pblk);
 		err = z_erofs_get_extent_compressedlen(&m, initial_lcn);
@@ -617,7 +616,7 @@ static int z_erofs_map_blocks_ext(struct inode *inode,
 	if (lstart < lend) {
 		map->m_la = lstart;
 		if (last && (vi->z_advise & Z_EROFS_ADVISE_FRAGMENT_PCLUSTER)) {
-			map->m_flags |= EROFS_MAP_MAPPED | EROFS_MAP_FRAGMENT;
+			map->m_flags = EROFS_MAP_FRAGMENT;
 			vi->z_fragmentoff = map->m_plen;
 			if (recsz > offsetof(struct z_erofs_extent, pstart_lo))
 				vi->z_fragmentoff |= map->m_pa << 32;
@@ -797,7 +796,7 @@ static int z_erofs_iomap_begin_report(struct inode *inode, loff_t offset,
 	iomap->length = map.m_llen;
 	if (map.m_flags & EROFS_MAP_MAPPED) {
 		iomap->type = IOMAP_MAPPED;
-		iomap->addr = map.m_flags & EROFS_MAP_FRAGMENT ?
+		iomap->addr = map.m_flags & __EROFS_MAP_FRAGMENT ?
 			      IOMAP_NULL_ADDR : map.m_pa;
 	} else {
 		iomap->type = IOMAP_HOLE;