[PATCH v4 32/45] fs: fat: Support reading from a larger block size
Bin Meng
bmeng.cn at gmail.com
Thu Jul 13 12:49:04 CEST 2023
Hi Simon,
On Mon, Jun 19, 2023 at 8:02 PM Simon Glass <sjg at chromium.org> wrote:
>
> 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.
I am completely confused. The CDROM uses iso9660 file system. This has
nothing to do with FAT.
>
> 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).
>
> Signed-off-by: Simon Glass <sjg at chromium.org>
> ---
>
> (no changes since v2)
>
> Changes in v2:
> - Use log_warning() for the warning
>
> 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 d1476aa433d6..686b321163fb 100644
> --- a/fs/fat/fat.c
> +++ b/fs/fat/fat.c
> @@ -45,13 +45,93 @@ 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)
> @@ -68,7 +148,7 @@ 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;
> }
> @@ -213,7 +293,7 @@ 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;
> }
> @@ -267,7 +347,7 @@ 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;
> @@ -281,7 +361,7 @@ 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;
> @@ -294,7 +374,7 @@ 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;
> @@ -506,7 +586,7 @@ 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;
> }
> @@ -588,9 +668,14 @@ 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) {
> - log_err("FAT sector size mismatch (fs=%u, dev=%lu)\n",
> - mydata->sect_size, cur_part_info.blksz);
> - return -1;
> + if (IS_ENABLED(CONFIG_FAT_BLK_XLATE)) {
> + log_warning("FAT sector size mismatch (fs=%u, dev=%lu): translating for read-only\n",
> + mydata->sect_size, cur_part_info.blksz);
> + } else {
> + log_err("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) {
> log_err("FAT cluster size not set\n");
> @@ -848,7 +933,7 @@ 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 e2a9913f807a..95f7a60caa2b 100644
> --- a/fs/fat/fat_write.c
> +++ b/fs/fat/fat_write.c
> @@ -477,7 +477,7 @@ 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;
> }
> @@ -712,7 +712,8 @@ 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;
> @@ -778,7 +779,8 @@ 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;
Regards,
Bin
More information about the U-Boot
mailing list