Am 30. März 2023 23:32:22 MESZ schrieb Simon Glass <s...@chromium.org>:
>At present it is not possible to read from some CDROM drives since the
>FAT sector size does not match the media's block size. Add a conversion
>option for this, so that reading is possible.
>
>This does increase SPL size for read-only FAT support by 25 bytes but
>all but 6 are covered by the previous patch. We could reduce the
>overhead of this feature to 0 bytes by making the code uglier (using
>a static variable).
512 and 2048 are not the only physical sector sizes. Some hard drives use 4096.
This change deserves a test case.
Best regards
Heinrich
>
>Signed-off-by: Simon Glass <s...@chromium.org>
>---
>
> fs/fat/Kconfig | 13 ++++++
> fs/fat/fat.c | 107 ++++++++++++++++++++++++++++++++++++++++-----
> fs/fat/fat_write.c | 8 ++--
> 3 files changed, 114 insertions(+), 14 deletions(-)
>
>diff --git a/fs/fat/Kconfig b/fs/fat/Kconfig
>index 9bb11eac9f7a..b0aa888c6cc4 100644
>--- a/fs/fat/Kconfig
>+++ b/fs/fat/Kconfig
>@@ -22,3 +22,16 @@ config FS_FAT_MAX_CLUSTSIZE
> is the smallest amount of disk space that can be used to hold a
> file. Unless you have an extremely tight memory memory constraints,
> leave the default.
>+
>+config FAT_BLK_XLATE
>+ bool "Enable FAT filesystem on a device with a larger block size"
>+ depends on FS_FAT
>+ help
>+ This provides a simple translation mechanism for reading FAT
>+ filesystems which don't use the same sector size as the underlying
>+ media. For example, the FAT filesystem may use 512 bytes but the
>+ media uses 2048, e.g. on a CDROM drive.
>+
>+ This only supports the case where the FAT filesystem's sector size is
>+ smaller than the media's block size. It does not support creating or
>+ writing files.
>diff --git a/fs/fat/fat.c b/fs/fat/fat.c
>index f0df7988e172..02c6d55a99b3 100644
>--- a/fs/fat/fat.c
>+++ b/fs/fat/fat.c
>@@ -43,13 +43,93 @@ static struct disk_partition cur_part_info;
> #define DOS_FS_TYPE_OFFSET 0x36
> #define DOS_FS32_TYPE_OFFSET 0x52
>
>-static int disk_read(__u32 block, __u32 nr_blocks, void *buf)
>+/**
>+ * disk_read_conv() - Read blocks and break them into smaller ones
>+ *
>+ * This is used when the FAT filesystem is hosted on a block device with a
>+ * block size greated than 512 bytes, e.g. the 2048 bytes of a CDROM drive. It
>+ * reads the blocks into a buffer and pulls out what is requested by the
>calling
>+ * function.
>+ *
>+ * It uses an internal 2KB buffer on the stack.
>+ *
>+ * @mydata: Filesystem information
>+ * @block: Block number to read, in terms of mydata->sect_size
>+ * @nr_blocks: Number of blocks to read, in terms of mydata->sect_size
>+ * @buf: Buffer for data
>+ */
>+static int disk_read_conv(fsdata *mydata, __u32 block, __u32 nr_blocks,
>+ void *buf)
>+{
>+ uint factor, whole, remain, upto;
>+ ulong base, index;
>+ uint to_copy;
>+ u8 tbuf[2048];
>+ int ret;
>+
>+ log_debug("mydata %x, cur_dev %lx, block %x, nr_block %x\n",
>+ mydata->sect_size, cur_dev->blksz, block, nr_blocks);
>+ if (mydata->sect_size > cur_dev->blksz ||
>+ cur_dev->blksz > sizeof(tbuf)) {
>+ log_err("Block size %lx not supported\n", cur_dev->blksz);
>+ return -EIO;
>+ }
>+ factor = cur_dev->blksz / mydata->sect_size;
>+
>+ /* get the first partial block */
>+ base = cur_part_info.start + block / factor;
>+ index = block % factor;
>+ log_debug("cur_part_info.start %llx, block %x, base %lx, index %lx\n",
>+ (unsigned long long)cur_part_info.start, block, base, index);
>+ ret = blk_dread(cur_dev, base, 1, tbuf);
>+ if (ret != 1)
>+ return -EIO;
>+
>+ to_copy = min((ulong)nr_blocks, factor - index);
>+ log_debug("to_copy %x\n", to_copy);
>+ memcpy(buf, tbuf + index * mydata->sect_size,
>+ to_copy * mydata->sect_size);
>+ upto = to_copy;
>+
>+ /* load any whole blocks */
>+ remain = nr_blocks - upto;
>+ whole = remain / factor;
>+ log_debug("factor %x, whole %x, remain %x\n", factor, whole, remain);
>+ if (whole) {
>+ ret = blk_dread(cur_dev, base + 1, whole,
>+ buf + upto * mydata->sect_size);
>+ if (ret != whole)
>+ return -EIO;
>+ upto += whole * factor;
>+ remain = nr_blocks - upto;
>+ }
>+
>+ /* load any blocks at the end */
>+ log_debug("end: remain %x\n", remain);
>+ if (remain) {
>+ ret = blk_dread(cur_dev, base + 1 + whole, 1, tbuf);
>+ if (ret != 1)
>+ return -EIO;
>+ memcpy(buf + upto * mydata->sect_size, tbuf,
>+ remain * mydata->sect_size);
>+ upto += remain;
>+ }
>+
>+ return upto;
>+}
>+
>+static int disk_read(fsdata *mydata, __u32 block, __u32 nr_blocks, void *buf)
> {
> ulong ret;
>
> if (!cur_dev)
> return -1;
>
>+ /* support converting from a larger block size */
>+ if (IS_ENABLED(CONFIG_FAT_BLK_XLATE) && mydata &&
>+ mydata->sect_size != cur_dev->blksz)
>+ return disk_read_conv(mydata, block, nr_blocks, buf);
>+
> ret = blk_dread(cur_dev, cur_part_info.start + block, nr_blocks, buf);
>
> if (ret != nr_blocks)
>@@ -66,7 +146,7 @@ int fat_set_blk_dev(struct blk_desc *dev_desc, struct
>disk_partition *info)
> cur_part_info = *info;
>
> /* Make sure it has a valid FAT header */
>- if (disk_read(0, 1, buffer) != 1) {
>+ if (disk_read(NULL, 0, 1, buffer) != 1) {
> cur_dev = NULL;
> return -1;
> }
>@@ -211,7 +291,7 @@ static __u32 get_fatent(fsdata *mydata, __u32 entry)
> if (flush_dirty_fat_buffer(mydata) < 0)
> return -1;
>
>- if (disk_read(startblock, getsize, bufptr) < 0) {
>+ if (disk_read(mydata, startblock, getsize, bufptr) < 0) {
> debug("Error reading FAT blocks\n");
> return ret;
> }
>@@ -265,7 +345,7 @@ get_cluster(fsdata *mydata, __u32 clustnum, __u8 *buffer,
>unsigned long size)
> debug("FAT: Misaligned buffer address (%p)\n", buffer);
>
> while (size >= mydata->sect_size) {
>- ret = disk_read(startsect++, 1, tmpbuf);
>+ ret = disk_read(mydata, startsect++, 1, tmpbuf);
> if (ret != 1) {
> debug("Error reading data (got %d)\n", ret);
> return -1;
>@@ -279,7 +359,7 @@ get_cluster(fsdata *mydata, __u32 clustnum, __u8 *buffer,
>unsigned long size)
> __u32 bytes_read;
> __u32 sect_count = size / mydata->sect_size;
>
>- ret = disk_read(startsect, sect_count, buffer);
>+ ret = disk_read(mydata, startsect, sect_count, buffer);
> if (ret != sect_count) {
> debug("Error reading data (got %d)\n", ret);
> return -1;
>@@ -292,7 +372,7 @@ get_cluster(fsdata *mydata, __u32 clustnum, __u8 *buffer,
>unsigned long size)
> if (size) {
> ALLOC_CACHE_ALIGN_BUFFER(__u8, tmpbuf, mydata->sect_size);
>
>- ret = disk_read(startsect, 1, tmpbuf);
>+ ret = disk_read(mydata, startsect, 1, tmpbuf);
> if (ret != 1) {
> debug("Error reading data (got %d)\n", ret);
> return -1;
>@@ -504,7 +584,7 @@ read_bootsectandvi(boot_sector *bs, volume_info *volinfo,
>int *fatsize)
> return -1;
> }
>
>- if (disk_read(0, 1, block) < 0) {
>+ if (disk_read(NULL, 0, 1, block) < 0) {
> debug("Error: reading block\n");
> goto fail;
> }
>@@ -586,9 +666,14 @@ static int get_fs_info(fsdata *mydata)
> mydata->sect_size = (bs.sector_size[1] << 8) + bs.sector_size[0];
> mydata->clust_size = bs.cluster_size;
> if (mydata->sect_size != cur_part_info.blksz) {
>- printf("** FAT sector size mismatch (fs=%hu, dev=%lu)\n",
>- mydata->sect_size, cur_part_info.blksz);
>- return -1;
>+ if (IS_ENABLED(CONFIG_FAT_BLK_XLATE)) {
>+ printf("Warning: FAT sector size mismatch (fs=%u,
>dev=%lu): translating for read-only\n",
>+ mydata->sect_size, cur_part_info.blksz);
>+ } else {
>+ printf("** FAT sector size mismatch (fs=%u, dev=%lu),
>see CONFIG_FAT_BLK_XLATE\n",
>+ mydata->sect_size, cur_part_info.blksz);
>+ return -1;
>+ }
> }
> if (mydata->clust_size == 0) {
> printf("** FAT cluster size not set\n");
>@@ -846,7 +931,7 @@ void *fat_next_cluster(fat_itr *itr, unsigned int *nbytes)
> * dent at a time and iteratively constructing the vfat long
> * name.
> */
>- ret = disk_read(sect, read_size, itr->block);
>+ ret = disk_read(itr->fsdata, sect, read_size, itr->block);
> if (ret < 0) {
> debug("Error: reading block\n");
> return NULL;
>diff --git a/fs/fat/fat_write.c b/fs/fat/fat_write.c
>index 4d2d4db07fa6..baef52af6363 100644
>--- a/fs/fat/fat_write.c
>+++ b/fs/fat/fat_write.c
>@@ -474,7 +474,7 @@ static int set_fatent_value(fsdata *mydata, __u32 entry,
>__u32 entry_value)
>
> startblock += mydata->fat_sect;
>
>- if (disk_read(startblock, getsize, bufptr) < 0) {
>+ if (disk_read(NULL, startblock, getsize, bufptr) < 0) {
> debug("Error reading FAT blocks\n");
> return -1;
> }
>@@ -709,7 +709,8 @@ get_set_cluster(fsdata *mydata, __u32 clustnum, loff_t
>pos, __u8 *buffer,
> /* partial write at beginning */
> if (pos) {
> wsize = min(bytesperclust - pos, size);
>- ret = disk_read(startsect, mydata->clust_size, tmpbuf_cluster);
>+ ret = disk_read(NULL, startsect, mydata->clust_size,
>+ tmpbuf_cluster);
> if (ret != mydata->clust_size) {
> debug("Error reading data (got %d)\n", ret);
> return -1;
>@@ -775,7 +776,8 @@ get_set_cluster(fsdata *mydata, __u32 clustnum, loff_t
>pos, __u8 *buffer,
> /* partial write at end */
> if (size) {
> wsize = size;
>- ret = disk_read(startsect, mydata->clust_size, tmpbuf_cluster);
>+ ret = disk_read(NULL, startsect, mydata->clust_size,
>+ tmpbuf_cluster);
> if (ret != mydata->clust_size) {
> debug("Error reading data (got %d)\n", ret);
> return -1;
