[PATCH 1/2] fs/erofs: Add support for EROFS

* [PATCH 1/2] fs/erofs: Add support for EROFS
@ 2023-07-16 16:03 Yifan Zhao
  2023-07-17  3:51 ` Glenn Washburn
  0 siblings, 1 reply; 11+ messages in thread
From: Yifan Zhao @ 2023-07-16 16:03 UTC (permalink / raw
  To: grub-devel; +Cc: hsiangkao, jefflexu, Yifan Zhao

EROFS is a lightweight read-only filesystem designed for performance which
has already been widely used in several scenarios, such as Android system
partitions, container images, and rootfs for embedded devices.

This patch brings EROFS uncompressed support. Now, it's possible to boot
directly through GRUB with an EROFS rootfs.

EROFS compressed support will be developed later since it has more work
to polish.

Signed-off-by: Yifan Zhao <zhaoyifan@sjtu.edu.cn>
---
The link here shows how to boot the kernel from the EROFS partition with this patch.
https://precious-celery-715.notion.site/Demo-of-booting-kernel-in-a-EROFS-partition-c6d199f937a2489bafd03d3083c294b5

 INSTALL                     |   8 +-
 Makefile.util.def           |   1 +
 docs/grub.texi              |   4 +-
 grub-core/Makefile.core.def |   5 +
 grub-core/fs/erofs.c        | 971 ++++++++++++++++++++++++++++++++++++
 grub-core/kern/misc.c       |  14 +
 include/grub/misc.h         |   1 +
 7 files changed, 998 insertions(+), 6 deletions(-)
 create mode 100644 grub-core/fs/erofs.c

diff --git a/INSTALL b/INSTALL
index b93fe9c61..1939e4745 100644
--- a/INSTALL
+++ b/INSTALL
@@ -77,15 +77,15 @@ Prerequisites for make-check:
 
 * If running a Linux kernel the following modules must be loaded:
   - fuse, loop
-  - btrfs, ext4, f2fs, fat, hfs, hfsplus, jfs, mac-roman, minix, nilfs2,
+  - btrfs, erofs, ext4, f2fs, fat, hfs, hfsplus, jfs, mac-roman, minix, nilfs2,
     reiserfs, udf, xfs
   - On newer kernels, the exfat kernel modules may be used instead of the
     exfat FUSE filesystem
 * The following are Debian named packages required mostly for the full
   suite of filesystem testing (but some are needed by other tests as well):
-  - btrfs-progs, dosfstools, e2fsprogs, exfat-utils, f2fs-tools, genromfs,
-    hfsprogs, jfsutils, nilfs-tools, ntfs-3g, reiserfsprogs, squashfs-tools,
-    reiserfsprogs, udftools, xfsprogs, zfs-fuse
+  - btrfs-progs, dosfstools, erofs_utils, e2fsprogs, exfat-utils, f2fs-tools,
+    genromfs, hfsprogs, jfsutils, nilfs-tools, ntfs-3g, reiserfsprogs,
+    squashfs-tools, reiserfsprogs, udftools, xfsprogs, zfs-fuse
   - exfat-fuse, if not using the exfat kernel module
   - gzip, lzop, xz-utils
   - attr, cpio, g++, gawk, parted, recode, tar, util-linux
diff --git a/Makefile.util.def b/Makefile.util.def
index 1e9a13d3e..ca2a32a7f 100644
--- a/Makefile.util.def
+++ b/Makefile.util.def
@@ -98,6 +98,7 @@ library = {
   common = grub-core/fs/cpio_be.c;
   common = grub-core/fs/odc.c;
   common = grub-core/fs/newc.c;
+  common = grub-core/fs/erofs.c;
   common = grub-core/fs/ext2.c;
   common = grub-core/fs/fat.c;
   common = grub-core/fs/exfat.c;
diff --git a/docs/grub.texi b/docs/grub.texi
index b81267980..20c119c96 100644
--- a/docs/grub.texi
+++ b/docs/grub.texi
@@ -361,7 +361,7 @@ blocklist notation. The currently supported filesystem types are @dfn{Amiga
 Fast FileSystem (AFFS)}, @dfn{AtheOS fs}, @dfn{BeFS},
 @dfn{BtrFS} (including raid0, raid1, raid10, gzip and lzo),
 @dfn{cpio} (little- and big-endian bin, odc and newc variants),
-@dfn{Linux ext2/ext3/ext4}, @dfn{DOS FAT12/FAT16/FAT32},
+@dfn{EROFS}, @dfn{Linux ext2/ext3/ext4}, @dfn{DOS FAT12/FAT16/FAT32},
 @dfn{exFAT}, @dfn{F2FS}, @dfn{HFS}, @dfn{HFS+},
 @dfn{ISO9660} (including Joliet, Rock-ridge and multi-chunk files),
 @dfn{JFS}, @dfn{Minix fs} (versions 1, 2 and 3), @dfn{nilfs2},
@@ -6212,7 +6212,7 @@ assumed to be encoded in UTF-8.
 NTFS, JFS, UDF, HFS+, exFAT, long filenames in FAT, Joliet part of
 ISO9660 are treated as UTF-16 as per specification. AFS and BFS are read
 as UTF-8, again according to specification. BtrFS, cpio, tar, squash4, minix,
-minix2, minix3, ROMFS, ReiserFS, XFS, ext2, ext3, ext4, FAT (short names),
+minix2, minix3, ROMFS, ReiserFS, XFS, EROFS, ext2, ext3, ext4, FAT (short names),
 F2FS, RockRidge part of ISO9660, nilfs2, UFS1, UFS2 and ZFS are assumed
 to be UTF-8. This might be false on systems configured with legacy charset
 but as long as the charset used is superset of ASCII you should be able to
diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
index d2cf29584..eccf9b6cf 100644
--- a/grub-core/Makefile.core.def
+++ b/grub-core/Makefile.core.def
@@ -1438,6 +1438,11 @@ module = {
   common = fs/odc.c;
 };
 
+module = {
+  name = erofs;
+  common = fs/erofs.c;
+};
+
 module = {
   name = ext2;
   common = fs/ext2.c;
diff --git a/grub-core/fs/erofs.c b/grub-core/fs/erofs.c
new file mode 100644
index 000000000..f1366ce05
--- /dev/null
+++ b/grub-core/fs/erofs.c
@@ -0,0 +1,971 @@
+/* erofs.c - Enhanced Read-Only File System */
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2023 Free Software Foundation, Inc.
+ *
+ *  GRUB is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  GRUB is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <grub/disk.h>
+#include <grub/dl.h>
+#include <grub/err.h>
+#include <grub/file.h>
+#include <grub/fs.h>
+#include <grub/fshelp.h>
+#include <grub/misc.h>
+#include <grub/mm.h>
+#include <grub/safemath.h>
+#include <grub/types.h>
+
+GRUB_MOD_LICENSE ("GPLv3+");
+
+#define ROUND_UP(x, y) ({ grub_divmod64 (x + (y - 1), y, NULL) * y; })
+
+#define EROFS_SUPER_OFFSET (1024)
+#define EROFS_MAGIC 0xE0F5E1E2
+#define EROFS_ISLOTBITS (5)
+
+#define EROFS_FEATURE_INCOMPAT_CHUNKED_FILE 0x00000004
+#define EROFS_ALL_FEATURE_INCOMPAT (EROFS_FEATURE_INCOMPAT_CHUNKED_FILE)
+
+struct grub_erofs_super
+{
+  grub_uint32_t magic;
+  grub_uint32_t checksum;
+  grub_uint32_t feature_compat;
+  grub_uint8_t blkszbits;
+  grub_uint8_t sb_extslots;
+
+  grub_uint16_t root_nid;
+  grub_uint64_t inos;
+
+  grub_uint64_t build_time;
+  grub_uint32_t build_time_nsec;
+  grub_uint32_t blocks;
+  grub_uint32_t meta_blkaddr;
+  grub_uint32_t xattr_blkaddr;
+  grub_uint8_t uuid[16];
+  grub_uint8_t volume_name[16];
+  grub_uint32_t feature_incompat;
+
+  union
+  {
+    grub_uint16_t available_compr_algs;
+    grub_uint16_t lz4_max_distance;
+  } GRUB_PACKED u1;
+
+  grub_uint16_t extra_devices;
+  grub_uint16_t devt_slotoff;
+  grub_uint8_t dirblkbits;
+  grub_uint8_t xattr_prefix_count;
+  grub_uint32_t xattr_prefix_start;
+  grub_uint64_t packed_nid;
+  grub_uint8_t reserved2[24];
+} GRUB_PACKED;
+
+#define EROFS_INODE_LAYOUT_COMPACT 0
+#define EROFS_INODE_LAYOUT_EXTENDED 1
+
+enum
+{
+  EROFS_INODE_FLAT_PLAIN = 0,
+  EROFS_INODE_COMPRESSED_FULL = 1,
+  EROFS_INODE_FLAT_INLINE = 2,
+  EROFS_INODE_COMPRESSED_COMPACT = 3,
+  EROFS_INODE_CHUNK_BASED = 4,
+  EROFS_INODE_DATALAYOUT_MAX
+};
+
+#define EROFS_I_VERSION_MASKS 0x01
+#define EROFS_I_DATALAYOUT_MASKS 0x07
+
+#define EROFS_I_VERSION_BIT 0
+#define EROFS_I_DATALAYOUT_BIT 1
+
+struct grub_erofs_inode_chunk_info
+{
+  grub_uint16_t format;
+  grub_uint16_t reserved;
+} GRUB_PACKED;
+
+#define EROFS_CHUNK_FORMAT_BLKBITS_MASK 0x001F
+#define EROFS_CHUNK_FORMAT_INDEXES 0x0020
+
+#define EROFS_BLOCK_MAP_ENTRY_SIZE 4
+
+#define EROFS_NULL_ADDR -1
+
+struct grub_erofs_inode_chunk_index
+{
+  grub_uint16_t advise;
+  grub_uint16_t device_id;
+  grub_uint32_t blkaddr;
+};
+
+union grub_erofs_inode_i_u
+{
+  grub_uint32_t compressed_blocks;
+  grub_uint32_t raw_blkaddr;
+
+  grub_uint32_t rdev;
+
+  struct grub_erofs_inode_chunk_info c;
+};
+
+struct grub_erofs_inode_compact
+{
+  grub_uint16_t i_format;
+
+  grub_uint16_t i_xattr_icount;
+  grub_uint16_t i_mode;
+  grub_uint16_t i_nlink;
+  grub_uint32_t i_size;
+  grub_uint32_t i_reserved;
+
+  union grub_erofs_inode_i_u i_u;
+
+  grub_uint32_t i_ino;
+  grub_uint16_t i_uid;
+  grub_uint16_t i_gid;
+  grub_uint32_t i_reserved2;
+} GRUB_PACKED;
+
+struct grub_erofs_inode_extended
+{
+  grub_uint16_t i_format;
+
+  grub_uint16_t i_xattr_icount;
+  grub_uint16_t i_mode;
+  grub_uint16_t i_reserved;
+  grub_uint64_t i_size;
+
+  union grub_erofs_inode_i_u i_u;
+
+  grub_uint32_t i_ino;
+
+  grub_uint32_t i_uid;
+  grub_uint32_t i_gid;
+  grub_uint64_t i_mtime;
+  grub_uint32_t i_mtime_nsec;
+  grub_uint32_t i_nlink;
+  grub_uint8_t i_reserved2[16];
+} GRUB_PACKED;
+
+enum
+{
+  EROFS_FT_UNKNOWN,
+  EROFS_FT_REG_FILE,
+  EROFS_FT_DIR,
+  EROFS_FT_CHRDEV,
+  EROFS_FT_BLKDEV,
+  EROFS_FT_FIFO,
+  EROFS_FT_SOCK,
+  EROFS_FT_SYMLINK,
+  EROFS_FT_MAX
+};
+
+#define EROFS_NAME_LEN 255
+
+struct grub_erofs_dirent
+{
+  grub_uint64_t nid;
+  grub_uint16_t nameoff;
+  grub_uint8_t file_type;
+  grub_uint8_t reserved;
+} GRUB_PACKED;
+
+enum
+{
+  BH_Meta,
+  BH_Mapped,
+};
+
+#define EROFS_MAP_MAPPED (1 << BH_Mapped)
+
+struct grub_erofs_map_blocks
+{
+  grub_off_t m_pa, m_la;
+  grub_off_t m_plen, m_llen;
+  grub_uint32_t m_flags;
+};
+
+struct grub_erofs_xattr_ibody_header
+{
+  grub_uint32_t h_reserved;
+  grub_uint8_t h_shared_count;
+  grub_uint8_t h_reserved2[7];
+  grub_uint32_t h_shared_xattrs[0];
+};
+
+struct grub_fshelp_node
+{
+  struct grub_erofs_data *data;
+  struct grub_erofs_inode_extended inode;
+
+  grub_uint64_t ino;
+  grub_uint8_t inode_type;
+  grub_uint8_t inode_datalayout;
+
+  /* if the inode has been read into memory? */
+  bool inode_read;
+};
+
+struct grub_erofs_data
+{
+  grub_disk_t disk;
+  struct grub_erofs_super sb;
+
+  struct grub_fshelp_node inode;
+};
+
+#define erofs_blocksz(data) (1u << data->sb.blkszbits)
+
+static inline grub_uint64_t
+erofs_iloc (grub_fshelp_node_t node)
+{
+  struct grub_erofs_super *sb = &node->data->sb;
+
+  return (grub_le_to_cpu32 (sb->meta_blkaddr) << sb->blkszbits) +
+         (node->ino << EROFS_ISLOTBITS);
+}
+
+static grub_err_t
+grub_erofs_read_inode (struct grub_erofs_data *data, grub_fshelp_node_t node)
+{
+  struct grub_erofs_inode_compact *dic;
+  grub_err_t err;
+  grub_uint64_t addr = erofs_iloc (node);
+
+  dic = (struct grub_erofs_inode_compact *)&node->inode;
+
+  err = grub_disk_read (data->disk, addr >> GRUB_DISK_SECTOR_BITS,
+                        addr & (GRUB_DISK_SECTOR_SIZE - 1),
+                        sizeof (struct grub_erofs_inode_compact), dic);
+  if (err)
+    return err;
+
+  node->inode_type =
+      (dic->i_format >> EROFS_I_VERSION_BIT) & EROFS_I_VERSION_MASKS;
+  node->inode_datalayout =
+      (dic->i_format >> EROFS_I_DATALAYOUT_BIT) & EROFS_I_DATALAYOUT_MASKS;
+
+  switch (node->inode_type)
+    {
+    case EROFS_INODE_LAYOUT_EXTENDED:
+      addr += sizeof (struct grub_erofs_inode_compact);
+      err = grub_disk_read (
+          data->disk, addr >> GRUB_DISK_SECTOR_BITS,
+          addr & (GRUB_DISK_SECTOR_SIZE - 1),
+          sizeof (struct grub_erofs_inode_extended) -
+              sizeof (struct grub_erofs_inode_compact),
+          (char *)dic + sizeof (struct grub_erofs_inode_compact));
+      if (err)
+        return err;
+      break;
+    case EROFS_INODE_LAYOUT_COMPACT:
+      break;
+    default:
+      return grub_error (GRUB_ERR_BAD_FS,
+                         "invalid inode version %u @ inode %" PRIuGRUB_UINT64_T,
+                         node->inode_type, node->ino);
+    }
+
+  node->inode_read = true;
+
+  return 0;
+}
+
+static inline grub_uint64_t
+erofs_inode_size (grub_fshelp_node_t node)
+{
+  return node->inode_type == EROFS_INODE_LAYOUT_COMPACT
+             ? sizeof (struct grub_erofs_inode_compact)
+             : sizeof (struct grub_erofs_inode_extended);
+}
+
+static inline grub_uint64_t
+erofs_inode_file_size (grub_fshelp_node_t node)
+{
+  struct grub_erofs_inode_compact *dic =
+      (struct grub_erofs_inode_compact *)&node->inode;
+
+  return node->inode_type == EROFS_INODE_LAYOUT_COMPACT
+             ? grub_le_to_cpu32 (dic->i_size)
+             : grub_le_to_cpu64 (node->inode.i_size);
+}
+
+static inline grub_uint32_t
+erofs_inode_xattr_ibody_size (grub_fshelp_node_t node)
+{
+  grub_uint16_t cnt = grub_le_to_cpu16 (node->inode.i_xattr_icount);
+
+  return cnt ? sizeof (struct grub_erofs_xattr_ibody_header) +
+                   (cnt - 1) * sizeof (grub_uint32_t)
+             : 0;
+}
+
+static inline grub_uint64_t
+erofs_inode_mtime (grub_fshelp_node_t node)
+{
+  return node->inode_type == EROFS_INODE_LAYOUT_COMPACT
+             ? grub_le_to_cpu64 (node->data->sb.build_time)
+             : grub_le_to_cpu64 (node->inode.i_mtime);
+}
+
+static grub_err_t
+grub_erofs_map_blocks_flatmode (grub_fshelp_node_t node,
+                                struct grub_erofs_map_blocks *map)
+{
+  grub_off_t nblocks, lastblk, file_size;
+  grub_off_t tailendpacking =
+      (node->inode_datalayout == EROFS_INODE_FLAT_INLINE) ? 1 : 0;
+  grub_uint32_t blocksz = erofs_blocksz (node->data);
+
+  file_size = erofs_inode_file_size (node);
+  nblocks = grub_divmod64 (file_size + blocksz - 1, blocksz, NULL);
+  lastblk = nblocks - tailendpacking;
+
+  map->m_flags = EROFS_MAP_MAPPED;
+
+  if (map->m_la < lastblk * blocksz)
+    {
+      map->m_pa =
+          grub_le_to_cpu32 (node->inode.i_u.raw_blkaddr) * blocksz + map->m_la;
+      map->m_plen = lastblk * blocksz - map->m_la;
+    }
+  else if (tailendpacking)
+    {
+      map->m_pa = erofs_iloc (node) + erofs_inode_size (node) +
+                  erofs_inode_xattr_ibody_size (node) + map->m_la % blocksz;
+      map->m_plen = file_size - map->m_la;
+
+      if (map->m_pa % blocksz + map->m_plen > blocksz)
+        return grub_error (
+            GRUB_ERR_BAD_FS,
+            "inline data cross block boundary @ inode %" PRIuGRUB_UINT64_T,
+            node->ino);
+    }
+  else
+    {
+      return grub_error (GRUB_ERR_BAD_FS,
+                         "internal error: invalid map->m_la=%" PRIuGRUB_UINT64_T
+                         " @ inode %" PRIuGRUB_UINT64_T,
+                         map->m_la, node->ino);
+    }
+
+  map->m_llen = map->m_plen;
+  return GRUB_ERR_NONE;
+}
+
+static grub_err_t
+grub_erofs_map_blocks_chunkmode (grub_fshelp_node_t node,
+                                 struct grub_erofs_map_blocks *map)
+{
+  grub_uint16_t chunk_format = grub_le_to_cpu16 (node->inode.i_u.c.format);
+  grub_off_t unit, pos;
+  grub_uint64_t chunknr;
+  grub_uint8_t chunkbits;
+  grub_err_t err;
+
+  if (chunk_format & EROFS_CHUNK_FORMAT_INDEXES)
+    unit = sizeof (struct grub_erofs_inode_chunk_index);
+  else
+    unit = EROFS_BLOCK_MAP_ENTRY_SIZE;
+
+  chunkbits = node->data->sb.blkszbits +
+              (chunk_format & EROFS_CHUNK_FORMAT_BLKBITS_MASK);
+
+  chunknr = map->m_la >> chunkbits;
+  pos = ROUND_UP (erofs_iloc (node) + erofs_inode_size (node) +
+                      erofs_inode_xattr_ibody_size (node),
+                  unit);
+  pos += chunknr * unit;
+
+  map->m_la = chunknr << chunkbits;
+  map->m_plen = grub_min (1ULL << chunkbits,
+                          ROUND_UP (erofs_inode_file_size (node) - map->m_la,
+                                    erofs_blocksz (node->data)));
+
+  if (chunk_format & EROFS_CHUNK_FORMAT_INDEXES)
+    {
+      struct grub_erofs_inode_chunk_index idx;
+      grub_uint32_t blkaddr;
+
+      err = grub_disk_read (node->data->disk, pos >> GRUB_DISK_SECTOR_BITS,
+                            pos & (GRUB_DISK_SECTOR_SIZE - 1), unit, &idx);
+      if (err)
+        return err;
+
+      blkaddr = grub_le_to_cpu32 (idx.blkaddr);
+
+      if (blkaddr == (grub_uint32_t)EROFS_NULL_ADDR)
+        {
+          map->m_pa = 0;
+          map->m_flags = 0;
+        }
+      else
+        {
+          map->m_pa = blkaddr << node->data->sb.blkszbits;
+          map->m_flags = EROFS_MAP_MAPPED;
+        }
+    }
+  else
+    {
+      grub_uint32_t blkaddr_le, blkaddr;
+
+      err =
+          grub_disk_read (node->data->disk, pos >> GRUB_DISK_SECTOR_BITS,
+                          pos & (GRUB_DISK_SECTOR_SIZE - 1), unit, &blkaddr_le);
+      if (err)
+        return err;
+
+      blkaddr = grub_le_to_cpu32 (blkaddr_le);
+      if (blkaddr == (grub_uint32_t)EROFS_NULL_ADDR)
+        {
+          map->m_pa = 0;
+          map->m_flags = 0;
+        }
+      else
+        {
+          map->m_pa = blkaddr << node->data->sb.blkszbits;
+          map->m_flags = EROFS_MAP_MAPPED;
+        }
+    }
+
+  map->m_llen = map->m_plen;
+  return GRUB_ERR_NONE;
+}
+
+static grub_err_t
+grub_erofs_map_blocks (grub_fshelp_node_t node,
+                       struct grub_erofs_map_blocks *map)
+{
+  if (map->m_la >= erofs_inode_file_size (node))
+    {
+      map->m_llen = map->m_plen = 0;
+      map->m_pa = 0;
+      map->m_flags = 0;
+      return GRUB_ERR_NONE;
+    }
+
+  if (node->inode_datalayout != EROFS_INODE_CHUNK_BASED)
+    return grub_erofs_map_blocks_flatmode (node, map);
+  else
+    return grub_erofs_map_blocks_chunkmode (node, map);
+}
+
+static grub_err_t
+grub_erofs_read_raw_data (grub_fshelp_node_t node, char *buf, grub_off_t size,
+                          grub_off_t offset, grub_off_t *bytes)
+{
+  struct grub_erofs_map_blocks map;
+  grub_err_t err;
+
+  if (bytes)
+    *bytes = 0;
+
+  if (!node->inode_read)
+    {
+      err = grub_erofs_read_inode (node->data, node);
+      if (err)
+        return err;
+    }
+
+  grub_memset (&map, 0, sizeof (map));
+
+  grub_off_t cur = offset;
+  while (cur < offset + size)
+    {
+      char *const estart = buf + cur - offset;
+      grub_off_t eend, moff = 0;
+
+      map.m_la = cur;
+      err = grub_erofs_map_blocks (node, &map);
+      if (err)
+        return err;
+
+      eend = grub_min (offset + size, map.m_la + map.m_llen);
+      if (!(map.m_flags & EROFS_MAP_MAPPED))
+        {
+          if (!map.m_llen)
+            {
+              /* reached EOF */
+              grub_memset (estart, 0, offset + size - cur);
+              cur = offset + size;
+              continue;
+            }
+
+          /* Hole */
+          grub_memset (estart, 0, eend - cur);
+          cur = eend;
+          if (bytes)
+            *bytes += eend - cur;
+          continue;
+        }
+
+      if (cur > map.m_la)
+        {
+          moff = cur - map.m_la;
+          map.m_la = cur;
+        }
+
+      err = grub_disk_read (node->data->disk,
+                            (map.m_pa + moff) >> GRUB_DISK_SECTOR_BITS,
+                            (map.m_pa + moff) & (GRUB_DISK_SECTOR_SIZE - 1),
+                            eend - map.m_la, estart);
+      if (err)
+        return err;
+
+      if (bytes)
+        *bytes += eend - map.m_la;
+
+      cur = eend;
+    }
+
+  return GRUB_ERR_NONE;
+}
+
+static int
+grub_erofs_iterate_dir (grub_fshelp_node_t dir,
+                        grub_fshelp_iterate_dir_hook_t hook, void *hook_data)
+{
+  grub_off_t offset = 0, file_size;
+  grub_err_t err;
+  grub_uint32_t blocksz = erofs_blocksz (dir->data);
+  char *buf;
+
+  if (!dir->inode_read)
+    {
+      err = grub_erofs_read_inode (dir->data, dir);
+      if (err)
+        return 0;
+    }
+
+  file_size = erofs_inode_file_size (dir);
+  buf = grub_malloc (blocksz);
+  if (!buf)
+    {
+      grub_error (GRUB_ERR_OUT_OF_MEMORY, "out of memory");
+      return 0;
+    }
+
+  while (offset < file_size)
+    {
+      grub_off_t maxsize = grub_min (blocksz, file_size - offset);
+      struct grub_erofs_dirent *de = (void *)buf, *end;
+      grub_uint16_t nameoff;
+
+      err = grub_erofs_read_raw_data (dir, buf, maxsize, offset, NULL);
+      if (err)
+        goto not_found;
+
+      nameoff = grub_le_to_cpu16 (de->nameoff);
+      if (nameoff < sizeof (struct grub_erofs_dirent) || nameoff > blocksz)
+        {
+          grub_error (GRUB_ERR_BAD_FS,
+                      "invalid de[0].nameoff %u @ inode %" PRIuGRUB_UINT64_T,
+                      nameoff, dir->ino);
+          goto not_found;
+        }
+
+      end = (struct grub_erofs_dirent *)((char *)de + nameoff);
+      while (de < end)
+        {
+          struct grub_fshelp_node *fdiro;
+          enum grub_fshelp_filetype type;
+          char filename[EROFS_NAME_LEN + 1];
+          unsigned int de_namelen;
+          const char *de_name;
+
+          fdiro = grub_malloc (sizeof (struct grub_fshelp_node));
+          if (!fdiro)
+            {
+              grub_error (GRUB_ERR_OUT_OF_MEMORY, "out of memory");
+              goto not_found;
+            }
+
+          fdiro->data = dir->data;
+          fdiro->ino = grub_le_to_cpu64 (de->nid);
+          fdiro->inode_read = false;
+
+          nameoff = grub_le_to_cpu16 (de->nameoff);
+          de_name = buf + nameoff;
+          if (de + 1 >= end)
+            de_namelen = grub_strnlen (de_name, maxsize - nameoff);
+          else
+            de_namelen = grub_le_to_cpu16 (de[1].nameoff) - nameoff;
+
+          grub_memcpy (filename, de_name, de_namelen);
+          filename[de_namelen] = '\0';
+
+          switch (grub_le_to_cpu16 (de->file_type))
+            {
+            case EROFS_FT_REG_FILE:
+            case EROFS_FT_BLKDEV:
+            case EROFS_FT_CHRDEV:
+            case EROFS_FT_FIFO:
+            case EROFS_FT_SOCK:
+              type = GRUB_FSHELP_REG;
+              break;
+            case EROFS_FT_DIR:
+              type = GRUB_FSHELP_DIR;
+              break;
+            case EROFS_FT_SYMLINK:
+              type = GRUB_FSHELP_SYMLINK;
+              break;
+            case EROFS_FT_UNKNOWN:
+            default:
+              type = GRUB_FSHELP_UNKNOWN;
+              break;
+            }
+
+          if (hook (filename, type, fdiro, hook_data))
+            {
+              grub_free (buf);
+              return 1;
+            }
+
+          ++de;
+        }
+
+      offset += maxsize;
+    }
+
+not_found:
+  grub_free (buf);
+  return 0;
+}
+
+static char *
+grub_erofs_read_symlink (grub_fshelp_node_t node)
+{
+  char *symlink;
+  grub_size_t sz;
+
+  if (!node->inode_read)
+    {
+      grub_erofs_read_inode (node->data, node);
+      if (grub_errno)
+        {
+          return NULL;
+        }
+    }
+
+  if (grub_add (erofs_inode_file_size (node), 1, &sz))
+    {
+      grub_error (GRUB_ERR_OUT_OF_RANGE, N_ ("overflow is detected"));
+      return NULL;
+    }
+
+  symlink = grub_malloc (sz);
+  if (!symlink)
+    return NULL;
+
+  grub_erofs_read_raw_data (node, symlink, sz - 1, 0, NULL);
+  if (grub_errno)
+    {
+      grub_free (symlink);
+      return NULL;
+    }
+
+  symlink[sz - 1] = '\0';
+  return symlink;
+}
+
+static struct grub_erofs_data *
+grub_erofs_mount (grub_disk_t disk, bool read_root)
+{
+  struct grub_erofs_super sb;
+  grub_err_t err;
+  struct grub_erofs_data *data;
+  grub_uint32_t feature;
+
+  err = grub_disk_read (disk, EROFS_SUPER_OFFSET >> GRUB_DISK_SECTOR_BITS, 0,
+                        sizeof (sb), &sb);
+  if (grub_errno == GRUB_ERR_OUT_OF_RANGE)
+    grub_error (GRUB_ERR_BAD_FS, "not a valid erofs filesystem");
+  if (err)
+    return NULL;
+  if (sb.magic != grub_cpu_to_le32_compile_time (EROFS_MAGIC))
+    {
+      grub_error (GRUB_ERR_BAD_FS, "not a valid erofs filesystem");
+      return NULL;
+    }
+
+  feature = grub_le_to_cpu32 (sb.feature_incompat);
+  if (feature & ~EROFS_ALL_FEATURE_INCOMPAT)
+    {
+      grub_error (GRUB_ERR_BAD_FS, "unsupported features: 0x%x",
+                  feature & ~EROFS_ALL_FEATURE_INCOMPAT);
+      return NULL;
+    }
+
+  data = grub_malloc (sizeof (*data));
+  if (!data)
+    {
+      grub_error (GRUB_ERR_OUT_OF_MEMORY, "out of memory");
+      return NULL;
+    }
+
+  data->disk = disk;
+  data->sb = sb;
+
+  if (read_root)
+    {
+      data->inode.data = data;
+      data->inode.ino = grub_le_to_cpu16 (sb.root_nid);
+      err = grub_erofs_read_inode (data, &data->inode);
+      if (err)
+        {
+          grub_free (data);
+          return NULL;
+        }
+    }
+
+  return data;
+}
+
+/* Context for grub_erofs_dir. */
+struct grub_erofs_dir_ctx
+{
+  grub_fs_dir_hook_t hook;
+  void *hook_data;
+  struct grub_erofs_data *data;
+};
+
+/* Helper for grub_erofs_dir. */
+static int
+grub_erofs_dir_iter (const char *filename, enum grub_fshelp_filetype filetype,
+                     grub_fshelp_node_t node, void *data)
+{
+  struct grub_erofs_dir_ctx *ctx = data;
+  struct grub_dirhook_info info;
+
+  grub_memset (&info, 0, sizeof (info));
+  if (!node->inode_read)
+    {
+      grub_erofs_read_inode (ctx->data, node);
+      grub_errno = GRUB_ERR_NONE;
+    }
+
+  if (node->inode_read)
+    {
+      info.mtimeset = 1;
+      info.mtime = erofs_inode_mtime (node);
+    }
+
+  info.dir = ((filetype & GRUB_FSHELP_TYPE_MASK) == GRUB_FSHELP_DIR);
+  grub_free (node);
+  return ctx->hook (filename, &info, ctx->hook_data);
+}
+
+static grub_err_t
+grub_erofs_dir (grub_device_t device, const char *path, grub_fs_dir_hook_t hook,
+                void *hook_data)
+{
+  grub_fshelp_node_t fdiro = NULL;
+  struct grub_erofs_dir_ctx ctx = {
+      .hook = hook,
+      .hook_data = hook_data,
+  };
+
+  ctx.data = grub_erofs_mount (device->disk, true);
+  if (!ctx.data)
+    goto fail;
+
+  grub_fshelp_find_file (path, &ctx.data->inode, &fdiro, grub_erofs_iterate_dir,
+                         grub_erofs_read_symlink, GRUB_FSHELP_DIR);
+  if (grub_errno)
+    goto fail;
+
+  grub_erofs_iterate_dir (fdiro, grub_erofs_dir_iter, &ctx);
+
+fail:
+  if (fdiro != &ctx.data->inode)
+    grub_free (fdiro);
+  grub_free (ctx.data);
+
+  return grub_errno;
+}
+
+static grub_err_t
+grub_erofs_open (grub_file_t file, const char *name)
+{
+  struct grub_erofs_data *data;
+  struct grub_fshelp_node *fdiro = 0;
+  grub_err_t err;
+
+  data = grub_erofs_mount (file->device->disk, true);
+  if (!data)
+    {
+      err = grub_errno;
+      goto fail;
+    }
+
+  err =
+      grub_fshelp_find_file (name, &data->inode, &fdiro, grub_erofs_iterate_dir,
+                             grub_erofs_read_symlink, GRUB_FSHELP_REG);
+  if (err)
+    goto fail;
+
+  if (!fdiro->inode_read)
+    {
+      err = grub_erofs_read_inode (data, fdiro);
+      if (err)
+        goto fail;
+    }
+
+  grub_memcpy (&data->inode, fdiro, sizeof (*fdiro));
+  grub_free (fdiro);
+
+  file->data = data;
+  file->size = erofs_inode_file_size (&data->inode);
+
+  return GRUB_ERR_NONE;
+
+fail:
+  if (fdiro != &data->inode)
+    grub_free (fdiro);
+  grub_free (data);
+
+  return err;
+}
+
+static grub_ssize_t
+grub_erofs_read (grub_file_t file, char *buf, grub_size_t len)
+{
+  struct grub_erofs_data *data = file->data;
+  struct grub_fshelp_node *inode = &data->inode;
+  grub_off_t off = file->offset, ret = 0;
+  grub_off_t file_size;
+
+  if (!inode->inode_read)
+    {
+      grub_erofs_read_inode (data, inode);
+      if (grub_errno)
+        {
+          ret = 0;
+          grub_error (GRUB_ERR_IO, "cannot read @ inode %" PRIuGRUB_UINT64_T,
+                      inode->ino);
+          goto end;
+        }
+    }
+
+  file_size = erofs_inode_file_size (inode);
+
+  if (off >= file_size)
+    goto end;
+
+  if (off + len > file_size)
+    len = file_size - off;
+
+  grub_erofs_read_raw_data (inode, buf, len, off, &ret);
+  if (grub_errno)
+    {
+      ret = 0;
+      grub_error (GRUB_ERR_IO, "cannot read file @ inode %" PRIuGRUB_UINT64_T,
+                  inode->ino);
+      goto end;
+    }
+
+end:
+  return ret;
+}
+
+static grub_err_t
+grub_erofs_close (grub_file_t file)
+{
+  grub_free (file->data);
+
+  return GRUB_ERR_NONE;
+}
+
+static grub_err_t
+grub_erofs_uuid (grub_device_t device, char **uuid)
+{
+  struct grub_erofs_data *data = grub_erofs_mount (device->disk, false);
+
+  if (data)
+    *uuid = grub_xasprintf (
+        "%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%"
+        "02x",
+        data->sb.uuid[0], data->sb.uuid[1], data->sb.uuid[2], data->sb.uuid[3],
+        data->sb.uuid[4], data->sb.uuid[5], data->sb.uuid[6], data->sb.uuid[7],
+        data->sb.uuid[8], data->sb.uuid[9], data->sb.uuid[10],
+        data->sb.uuid[11], data->sb.uuid[12], data->sb.uuid[13],
+        data->sb.uuid[14], data->sb.uuid[15]);
+  else
+    *uuid = NULL;
+
+  grub_free (data);
+
+  return grub_errno;
+}
+
+static grub_err_t
+grub_erofs_label (grub_device_t device, char **label)
+{
+  struct grub_erofs_data *data = grub_erofs_mount (device->disk, false);
+
+  if (data)
+    *label = grub_strndup ((char *)data->sb.volume_name,
+                           sizeof (data->sb.volume_name));
+  else
+    *label = NULL;
+
+  grub_free (data);
+
+  return grub_errno;
+}
+
+static grub_err_t
+grub_erofs_mtime (grub_device_t device, grub_int64_t *tm)
+{
+  struct grub_erofs_data *data = grub_erofs_mount (device->disk, false);
+
+  if (!data)
+    *tm = 0;
+  else
+    *tm = grub_le_to_cpu64 (data->sb.build_time);
+
+  grub_free (data);
+
+  return grub_errno;
+}
+
+static struct grub_fs grub_erofs_fs = {
+    .name = "erofs",
+    .fs_dir = grub_erofs_dir,
+    .fs_open = grub_erofs_open,
+    .fs_read = grub_erofs_read,
+    .fs_close = grub_erofs_close,
+    .fs_uuid = grub_erofs_uuid,
+    .fs_label = grub_erofs_label,
+    .fs_mtime = grub_erofs_mtime,
+#ifdef GRUB_UTIL
+    .reserved_first_sector = 1,
+    .blocklist_install = 0,
+#endif
+    .next = 0,
+};
+
+GRUB_MOD_INIT (erofs)
+{
+  grub_fs_register (&grub_erofs_fs);
+}
+
+GRUB_MOD_FINI (erofs)
+{
+  grub_fs_unregister (&grub_erofs_fs);
+}
\ No newline at end of file
diff --git a/grub-core/kern/misc.c b/grub-core/kern/misc.c
index 2890aad49..66cbb3c5c 100644
--- a/grub-core/kern/misc.c
+++ b/grub-core/kern/misc.c
@@ -594,6 +594,20 @@ grub_strlen (const char *s)
   return p - s;
 }
 
+grub_size_t
+grub_strnlen (const char *s, grub_size_t n)
+{
+  const char *p = s;
+
+  if (n == 0)
+    return 0;
+
+  while (*p && n--)
+    p++;
+
+  return p - s;
+}
+
 static inline void
 grub_reverse (char *str)
 {
diff --git a/include/grub/misc.h b/include/grub/misc.h
index 1b35a167f..eb4aa55c1 100644
--- a/include/grub/misc.h
+++ b/include/grub/misc.h
@@ -335,6 +335,7 @@ char *EXPORT_FUNC(grub_strdup) (const char *s) WARN_UNUSED_RESULT;
 char *EXPORT_FUNC(grub_strndup) (const char *s, grub_size_t n) WARN_UNUSED_RESULT;
 void *EXPORT_FUNC(grub_memset) (void *s, int c, grub_size_t n);
 grub_size_t EXPORT_FUNC(grub_strlen) (const char *s) WARN_UNUSED_RESULT;
+grub_size_t EXPORT_FUNC(grub_strnlen) (const char *s, grub_size_t n) WARN_UNUSED_RESULT;
 
 /* Replace all `ch' characters of `input' with `with' and copy the
    result into `output'; return EOS address of `output'. */
-- 
2.41.0



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