Re: UDF filesystem image with Write-Once UDF Access Type

["Pali Rohár" <pali.rohar@gmail.com>]

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On Thursday 01 August 2019 10:38:00 Jan Kara wrote:
> On Thu 01-08-19 09:35:30, Jan Kara wrote:
> > > 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.

Hi!

Now I verified version from git master branch and it seems to work.

$ ./mkudffs/mkudffs --media-type=cdr --new-file /tmp/cdr 307200
filename=/tmp/cdr
label=LinuxUDF
uuid=1564648861319606
blocksize=2048
blocks=307200
udfrev=2.01
vatblock=319
start=0, blocks=16, type=RESERVED 
start=16, blocks=4, type=VRS 
start=20, blocks=76, type=USPACE 
start=96, blocks=16, type=MVDS 
start=112, blocks=16, type=USPACE 
start=128, blocks=1, type=LVID 
start=129, blocks=95, type=USPACE 
start=224, blocks=16, type=RVDS 
start=240, blocks=16, type=USPACE 
start=256, blocks=1, type=ANCHOR 
start=257, blocks=31, type=USPACE 
start=288, blocks=306912, type=PSPACE

$ ls -l -a /tmp/cdr
-rw-r----- 1 pali pali 655360 aug  1 10:41 /tmp/cdr

$ mkdir /mnt/cdr

$ sudo mount /tmp/cdr /mnt/cdr -o loop
mount: /dev/loop0 is write-protected, mounting read-only

$ dmesg | tail
[320934.128836] loop: module loaded
[320934.169960] UDF-fs: warning (device loop0): udf_load_vrs: No anchor found
[320934.169965] UDF-fs: Rescanning with blocksize 2048
[320934.177772] UDF-fs: warning (device loop0): udf_load_vrs: No anchor found
[320934.177777] UDF-fs: Rescanning with blocksize 2048
[320934.181206] UDF-fs: INFO Mounting volume 'LinuxUDF', timestamp 2019/08/01 10:41 (1078)

$ uname -rvm
4.9.0-9-amd64 #1 SMP Debian 4.9.168-1+deb9u4 (2019-07-19) x86_64


And CDR code was not modified since release 2.1. At time of releasing
version 2.1 I tested that cdr image created by mkudffs and burned to
CD-R disc can be correctly recognized and mounted by linux kernel.

> Hum, looks like a problem with mkudffs. Relevant debug messages look like:
> 
> UDF-fs: fs/udf/super.c:671:udf_check_vsd: Starting at sector 16 (2048 byte sectors)
> UDF-fs: fs/udf/super.c:824:udf_load_pvoldesc: recording time 2019/08/01 09:47 (1078)
> UDF-fs: fs/udf/super.c:836:udf_load_pvoldesc: volIdent[] = 'LinuxUDF'
> UDF-fs: fs/udf/super.c:844:udf_load_pvoldesc: volSetIdent[] = '1564645645200563LinuxUDF'
> UDF-fs: fs/udf/super.c:1462:udf_load_logicalvol: Partition (0:0) type 1 on volume 1
> UDF-fs: fs/udf/super.c:1462:udf_load_logicalvol: Partition (1:0) type 2 on volume 1
> UDF-fs: fs/udf/super.c:1471:udf_load_logicalvol: FileSet found in LogicalVolDesc at block=0, partition=1
> UDF-fs: fs/udf/super.c:1218:udf_load_partdesc: Searching map: (0 == 0)
> UDF-fs: fs/udf/super.c:1060:udf_fill_partdesc_info: Partition (0 type 1511) starts at physical 288, block length 524000
> UDF-fs: fs/udf/super.c:1060:udf_fill_partdesc_info: Partition (1 type 2012) starts at physical 288, block length 524000
> UDF-fs: fs/udf/misc.c:223:udf_read_tagged: location mismatch block 524287, tag 0 != 523999
> UDF-fs: error (device ubdb): udf_read_inode: (ino 524287) failed !bh
> 
> So the fact that location tag was 0 in block 524287 (which should contain
> VAT inode) suggests there's something fishy with how / where mkudffs
> creates the VAT inode. Can you have a look?
> 
> BTW, mkudffs messages look like:
> filename=/tmp/image
> label=LinuxUDF
> uuid=1564645645200563
> blocksize=2048
> blocks=524288
> udfrev=2.01
> vatblock=319
> start=0, blocks=16, type=RESERVED 
> start=16, blocks=4, type=VRS 
> start=20, blocks=76, type=USPACE 
> start=96, blocks=16, type=MVDS 
> start=112, blocks=16, type=USPACE 
> start=128, blocks=1, type=LVID 
> start=129, blocks=95, type=USPACE 
> start=224, blocks=16, type=RVDS 
> start=240, blocks=16, type=USPACE 
> start=256, blocks=1, type=ANCHOR 
> start=257, blocks=31, type=USPACE 
> start=288, blocks=524000, type=PSPACE 
> 
> which suggests that VAT was indeed allocated somewhere in the beginning of
> the partition.

For write-once media you are not able to modify size of UDF partition.
So if you are creating image for CD-R disc, you need to specify size of
UDF filesystem to match size of CD-R disc. VAT is always burned to the
last block of current track on CD-R.

Therefore if you had pre-allocated big image file for CD-R and then you
run mkudffs for cdr on it, you lost information what is the last used
block on that cdr image. Normally for optical drivers kernel use mmc
commands to retrieve last block of current session and based on it find
VAT. But image files loaded via /dev/loop are not optical drivers and
therefore do not have ability "hardware" ability to ask where is the
last used block. IIRC in this case kernel just fallback to the last
block of block device for VAT, which in this case is not correct.

What should help is to truncate image file to "correct" size after
running mkudffs with --media-type=cdr. Maybe mkudffs itself should do it
when was asked to create UDF filesystem for CD-R on existing image file.

-- 
Pali Rohár
pali.rohar@gmail.com

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