From: Simon Glass <simon.glass@canonical.com> Some block devices, such as LUKS-encrypted volumes mounted via blkmap_crypt, only support read access. When ext4l attempts to write the superblock during mount, the write fails and causes mount to fail. Add a way to detect this read-only device detection: - Test writes during mount by writing back the superblock data; if the write fails, mark the device as read-only - Update bdev_read_only() to return the actual read_only status - Update sb_rdonly() to check the SB_RDONLY flag This allows ext4l to successfully mount read-only devices like LUKS volumes for read access. We could perhaps have a read-only flag in the block device, but that is left for another day. Co-developed-by: Claude <noreply@anthropic.com> Signed-off-by: Simon Glass <simon.glass@canonical.com> --- fs/ext4l/ext4_uboot.h | 8 ++++---- fs/ext4l/interface.c | 14 ++++++++++++-- include/linux/fs.h | 1 + 3 files changed, 17 insertions(+), 6 deletions(-) diff --git a/fs/ext4l/ext4_uboot.h b/fs/ext4l/ext4_uboot.h index 00419fe834e..da59956eee8 100644 --- a/fs/ext4l/ext4_uboot.h +++ b/fs/ext4l/ext4_uboot.h @@ -315,8 +315,8 @@ extern struct user_namespace init_user_ns; /* might_sleep - stub */ #define might_sleep() do { } while (0) -/* sb_rdonly - U-Boot mounts filesystems read-write */ -#define sb_rdonly(sb) 0 +/* sb_rdonly - check if filesystem is mounted read-only */ +#define sb_rdonly(sb) ((sb)->s_flags & SB_RDONLY) /* Trace stubs */ #define trace_ext4_journal_start_inode(...) do { } while (0) @@ -687,10 +687,10 @@ struct super_block { struct list_head s_inodes; }; -/* Block device read-only check - stub */ +/* Block device read-only check */ static inline int bdev_read_only(struct block_device *bdev) { - return 0; + return bdev ? bdev->read_only : 0; } /* kuid_t and kgid_t - from linux/cred.h */ diff --git a/fs/ext4l/interface.c b/fs/ext4l/interface.c index 301e28af3b8..c60ea7db684 100644 --- a/fs/ext4l/interface.c +++ b/fs/ext4l/interface.c @@ -401,8 +401,6 @@ int ext4l_probe(struct blk_desc *fs_dev_desc, goto err_free_buf; } - free(buf); - /* Save device info for later operations */ ext4l_dev_desc = fs_dev_desc; if (fs_partition) @@ -411,6 +409,18 @@ int ext4l_probe(struct blk_desc *fs_dev_desc, /* Set block device for buffer I/O */ ext4l_set_blk_dev(fs_dev_desc, fs_partition); + /* + * Test if device supports writes by writing back the same data. + * If write returns 0, the device is read-only (e.g. LUKS/blkmap_crypt) + */ + if (blk_dwrite(fs_dev_desc, + (part_offset + BLOCK_SIZE) / fs_dev_desc->blksz, + 2, buf) != 2) { + sb->s_bdev->read_only = true; + sb->s_flags |= SB_RDONLY; + } + free(buf); + /* Mount the filesystem */ ret = ext4_fill_super(sb, fc); if (ret) { diff --git a/include/linux/fs.h b/include/linux/fs.h index 0bf0d3b0379..54c0148ee72 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -76,6 +76,7 @@ struct block_device { void *bd_disk; struct super_block *bd_super; dev_t bd_dev; + bool read_only; }; /* errseq functions - stubs */ -- 2.43.0