On Monday 13 January 2020 12:48:38 Jan Kara wrote: > Hello, > > On Sun 12-01-20 15:47:35, Pali Rohár wrote: > > Commit b085fbe2ef7fa (udf: Fix crash during mount) introduced check that > > UDF disk with PD_ACCESS_TYPE_REWRITABLE access type would not be able to > > mount in R/W mode. This commit was added in Linux 4.20. > > > > But most tools which generate UDF filesystem for CD-RW set access type > > to rewritable, so above change basically disallow usage of CD-RW discs > > formatted to UDF in R/W mode. > > > > Linux's cdrwtool and mkudffs (in all released versions), Windows Nero 6, > > NetBSD's newfs_udf -- all these tools uses rewritable access type for > > CD-RW media. > > > > In UDF 1.50, 2.00 and 2.01 specification there is no information which > > UDF access type should be used for CD-RW medias. > > > > In UDF 2.60, section 2.2.14.2 is written: > > > > A partition with Access Type 3 (rewritable) shall define a Freed > > Space Bitmap or a Freed Space Table, see 2.3.3. All other partitions > > shall not define a Freed Space Bitmap or a Freed Space Table. > > > > Rewritable partitions are used on media that require some form of > > preprocessing before re-writing data (for example legacy MO). Such > > partitions shall use Access Type 3. > > > > Overwritable partitions are used on media that do not require > > preprocessing before overwriting data (for example: CD-RW, DVD-RW, > > DVD+RW, DVD-RAM, BD-RE, HD DVD-Rewritable). Such partitions shall > > use Access Type 4. > > > > And in 6.14.1 (Properties of CD-MRW and DVD+MRW media and drives) is: > > > > The Media Type is Overwritable (partition Access Type 4, > > overwritable) > > > > Similar info is in UDF 2.50. > > Thanks for detailed info. Yes, UDF 2.60 spec is why I've added the check > you mentioned. I was not aware that the phrasing was not there in earlier > versions and frankly even the UDF 2.60 spec is already 15 years old... But > the fact that there are tools creating non-compliant disks certainly > changes the picture :) I tested also Nero Linux 4 (Nero provides free trial version which is fully working even in 2020) and it creates 1.50 CD-RW discs in the same way with Rewritable partition. Interestingly for 2.50 and 2.60 it does not use Overwritable, but Writeonce (yes, for CD-RW with Spartable). And because previous UDF specification do not say anything about it, I would not sat that those discs are non-compliant. Moreover, is there any tool (for Linux or other system) which uses Overwritable partition type for CD-RW discs? All which I tested uses Rewritable. > > So I think that UDF 2.60 is clear that for CD-RW medias (formatted in > > normal or MRW mode) should be used Overwritable access type. But all > > mentioned tools were probably written prior to existence of UDF 2.60 > > specifications, probably targeting only UDF 1.50 versions at that time. > > > > I checked that they use Unallocated Space Bitmap (and not Freed Space > > Bitmap), so writing to these filesystems should not be a problem. > > > > How to handle this situation? UDF 2.01 nor 1.50 does not say anything > > for access type on CD-RW and there are already tools which generates UDF > > 1.50 images which does not matches UDF 2.60 requirements. > > > > I think that the best would be to relax restrictions added in commit > > b085fbe2ef7fa to allow mounting mounting udf fs with rewritable access > > type in R/W mode if Freed Space Bitmap/Table is not used. > > > > I'm really not sure if existing udf implementations take CD-RW media > > with overwritable media type. E.g. prehistoric wrudf tool refuse to work > > with optical discs which have overwritable access type. I supports only > > UDF 1.50. > > Yeah, we should maintain compatibility with older tools where sanely > possible. So I agree with what you propose. Allow writing to > PD_ACCESS_TYPE_REWRITABLE disks if they don't use 'Freed Space > Bitmap/Table'. Will you send a patch or should I do the update? Could you do it, please? Also question is, what with those 2.50 CD-RW Writonce partitions and with Spartable which creates Nero Linux? -- Pali Rohár pali.rohar@xxxxxxxxx
