[PATCH v2] mkfs: support block map for blob devices

[Nithurshen]

Currently, using --blobdev to specify an extra device is restricted
from working with the block map chunk format. This was previously
noted as a task that could be implemented by mapping the device
blocks using a global address.

This patch implements this support by allowing the block map to
reference chunks residing on extra devices. This is achieved by:
1) Removing the -EINVAL check in mkfs/main.c.
2) Calculating the global startblk address for the block map by
   summing the blocks of the primary device and preceding devices.
3) Ensuring EROFS_CHUNK_FORMAT_INDEXES is only set if the user
   has not forced the block map format.
4) Updating erofs_inode_fixup_chunkformat to error out if the
   mapped address exceeds UINT32_MAX, as block maps cannot
   support 48-bit addressing.

In addition, erofs_map_dev() is updated to correctly identify the
device ID when a global block address is used with block maps,
enabling userspace tools to read these images.

Signed-off-by: Nithurshen <nithurshen.dev at gmail.com>
---
 lib/blobchunk.c | 34 ++++++++++++++++++++++++++++------
 lib/data.c      |  1 +
 mkfs/main.c     |  7 -------
 3 files changed, 29 insertions(+), 13 deletions(-)

diff --git a/lib/blobchunk.c b/lib/blobchunk.c
index 96c161b..fdcf4b3 100644
--- a/lib/blobchunk.c
+++ b/lib/blobchunk.c
@@ -159,7 +159,17 @@ void erofs_inode_fixup_chunkformat(struct erofs_inode *inode)
 		if (chunk->blkaddr == EROFS_NULL_ADDR)
 			continue;
 		if (chunk->device_id) {
-			if (chunk->blkaddr > UINT32_MAX) {
+			if (!(inode->u.chunkformat & EROFS_CHUNK_FORMAT_INDEXES)) {
+				erofs_blk_t mapped_blkaddr = inode->sbi->primarydevice_blocks;
+				unsigned int i;
+
+				for (i = 0; i < chunk->device_id - 1; i++)
+					mapped_blkaddr += inode->sbi->devs[i].blocks;
+				if (mapped_blkaddr + chunk->blkaddr > UINT32_MAX) {
+					erofs_err("block map cannot support addresses > UINT32_MAX");
+					return;
+				}
+			} else if (chunk->blkaddr > UINT32_MAX) {
 				_48bit = true;
 				break;
 			}
@@ -201,8 +211,16 @@ int erofs_write_chunk_indexes(struct erofs_inode *inode, struct erofs_vfile *vf,
 		if (chunk->blkaddr == EROFS_NULL_ADDR) {
 			startblk = EROFS_NULL_ADDR;
 		} else if (chunk->device_id) {
-			DBG_BUGON(!(inode->u.chunkformat & EROFS_CHUNK_FORMAT_INDEXES));
-			startblk = chunk->blkaddr;
+			if (inode->u.chunkformat & EROFS_CHUNK_FORMAT_INDEXES) {
+				startblk = chunk->blkaddr;
+			} else {
+				unsigned int i;
+
+				startblk = sbi->primarydevice_blocks;
+				for (i = 0; i < chunk->device_id - 1; i++)
+					startblk += sbi->devs[i].blocks;
+				startblk += chunk->blkaddr;
+			}
 			extent_start = EROFS_NULL_ADDR;
 		} else {
 			startblk = remapped_base + chunk->blkaddr;
@@ -324,7 +342,7 @@ int erofs_blob_write_chunked_file(struct erofs_inode *inode, int fd,
 	chunksize = 1ULL << chunkbits;
 	count = DIV_ROUND_UP(inode->i_size, chunksize);
 
-	if (sbi->extra_devices)
+	if (sbi->extra_devices && cfg.c_force_chunkformat != FORCE_INODE_BLOCK_MAP)
 		inode->u.chunkformat |= EROFS_CHUNK_FORMAT_INDEXES;
 	if (inode->u.chunkformat & EROFS_CHUNK_FORMAT_INDEXES)
 		unit = sizeof(struct erofs_inode_chunk_index);
@@ -494,8 +512,12 @@ int tarerofs_write_chunkes(struct erofs_inode *inode, erofs_off_t data_offset)
 	inode->u.chunkformat |= chunkbits - sbi->blkszbits;
 	if (sbi->extra_devices) {
 		device_id = 1;
-		inode->u.chunkformat |= EROFS_CHUNK_FORMAT_INDEXES;
-		unit = sizeof(struct erofs_inode_chunk_index);
+		if (cfg.c_force_chunkformat != FORCE_INODE_BLOCK_MAP)
+			inode->u.chunkformat |= EROFS_CHUNK_FORMAT_INDEXES;
+		if (inode->u.chunkformat & EROFS_CHUNK_FORMAT_INDEXES)
+			unit = sizeof(struct erofs_inode_chunk_index);
+		else
+			unit = EROFS_BLOCK_MAP_ENTRY_SIZE;
 		DBG_BUGON(erofs_blkoff(sbi, data_offset));
 		blkaddr = erofs_blknr(sbi, data_offset);
 	} else {
diff --git a/lib/data.c b/lib/data.c
index 6fd1389..5aeb0c1 100644
--- a/lib/data.c
+++ b/lib/data.c
@@ -184,6 +184,7 @@ int erofs_map_dev(struct erofs_sb_info *sbi, struct erofs_map_dev *map)
 			if (map->m_pa >= startoff &&
 			    map->m_pa < startoff + length) {
 				map->m_pa -= startoff;
+				map->m_deviceid = id + 1;
 				break;
 			}
 		}
diff --git a/mkfs/main.c b/mkfs/main.c
index 58c18f9..07ef086 100644
--- a/mkfs/main.c
+++ b/mkfs/main.c
@@ -1565,13 +1565,6 @@ static int mkfs_parse_options_cfg(struct erofs_importer_params *params,
 		return -EINVAL;
 	}
 
-	/* TODO: can be implemented with (deviceslot) mapped_blkaddr */
-	if (cfg.c_blobdev_path &&
-	    cfg.c_force_chunkformat == FORCE_INODE_BLOCK_MAP) {
-		erofs_err("--blobdev cannot work with block map currently");
-		return -EINVAL;
-	}
-
 	if (optind >= argc) {
 		erofs_err("missing argument: FILE");
 		return -EINVAL;
-- 
2.51.0