Hello! On Fri 12-07-19 12:02:24, Pali Rohár wrote: > I had discussion with Roald and based on his tests, Linux kernel udf.ko > driver mounts UDF filesystem image with Write-Once UDF Access Type as > normal read/write filesystem. > > I think this is a bug as Write-Once Access Type is defined that existing > blocks on filesystem cannot be rewritten. Only new blocks can be > appended after end of device. Basically it means special HW support from > underlying media, e.g. for optical medias packet-writing technique (or > ability to burn new session) and CDROM_LAST_WRITTEN ioctl to locate > "current" end of device. > > In my opinion without support for additional layer, kernel should treat > UDF Write-Once Access Type as read-only mount for userspace. And not > classic read/write mount. > > If you want to play with Write-Once Access Type, use recent version of > mkudffs and choose --media-type=cdr option, which generates UDF > filesystem suitable for CD-R (Write-Once Access Type with VAT and other > UDF options according to UDF specification). Reasonably recent kernels should have this bug fixed and mount such fs read only. That being said I've tested current upstream kernel with a media created with --media-type=cdr and mounting failed with: UDF-fs: error (device ubdb): udf_read_inode: (ino 524287) failed !bh UDF-fs: error (device ubdb): udf_read_inode: (ino 524286) failed !bh UDF-fs: error (device ubdb): udf_read_inode: (ino 524285) failed !bh UDF-fs: error (device ubdb): udf_read_inode: (ino 524284) failed !bh UDF-fs: Scanning with blocksize 2048 failed So there's something fishy either in the created image or the kernel... Didn't debug this further yet. > Also in git master of udftools has mkduffs now new option --read-only > which creates UDF image with Read-Only Access Type. I've tested this and the kernel properly mounts the image read-only. > It seems that udf.ko does not support updating VAT table, so probably it > should treat also filesystem with VAT as read-only too. This is definitely handled properly and we mount such fs read-only as well. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
