Messages in this thread | | | Date | Thu, 5 Jan 2023 10:45:47 -0700 | Subject | Re: Linux 6.2-rc1 | From | Jens Axboe <> |
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On 1/5/23 10:42?AM, Pali Roh?r wrote: > On Wednesday 04 January 2023 14:43:16 Jens Axboe wrote: >> On 1/4/23 2:32?PM, Linus Torvalds wrote: >>>> But here it is CD-RW media in read-write mode with kernel udf >>>> filesystem driver without any userspace involved (after proper >>>> formatting). >>> >>> ... but I'm not sure about direct writeable mount support. >>> >>> That may indeed be an area that only pktcdvd ended up doing. I've >>> never used it myself, even historically. >>> >>> Let's bring in more people. Because they may not have thought about >>> some RW UDF case. >> >> We did think about it, since that's the only reason for pktcdvd to >> exist. Basically what the driver does is ensure that any write is 32K in >> size, which is the size which can be written to media. It'll gather data >> as needed to make that happen. Thats it. Outside of that, it's just some >> setup and closing code. >> >> This obviously would be better to handle in userspace, all of it. Back >> when I wrote this driver, we didn't have a lot of the fancier stuff we >> have today. It could be done via ublk, for example, or something like >> that. >> >> The surprising bit here is: >> >> 1) Someone is still using this driver, and >> 2) It actually works! > > Yes, there are still users and userspace tools (cdrwtool / pktsetup) are > still receiving either small patches or issue reports. I think that it > was two years ago when cdrwtool received big fixups to support > formatting CD-RW discs on new CD/DVD drives. > >> While I'd love to nudge folks in other directions for this use case, and >> I strongly think that we should, it also doesn't seem fair to just yank >> it while folks are using it... But I'd like to VERY strongly encourage >> folks to come up with a new solution for this use case. It really isn't >> a solution that belongs in the kernel today. > > Linus in previous email wrote that he did "make SCSI commands generic" > work in past so direct usage of /dev/cdrom device works for CD-R burning > and read-only mounting.
Not quite sure what that refers to, as I'm pretty sure I did all of that work. But maybe Linus can refresh my memory here :-)
> So could not be (for example sr.c) driver extended to directly do > pktcdvd's work? So when somebody opens /dev/cdrom device in O_RDWR mode > and CD-RW medium is present then it would behave like pktcdvd device... > To have /dev/cdrom generic also for CD-RW write access.
As mentioned, I don't think this kind of code belongs in the kernel. sr or cdrom could easily be modified to support the necessary bits to handle a writeable open, but the grunt of the pktcdvd code deals with retrieving and writing out bigger chunks of data. And that part really does belong in userspace imho.
-- Jens Axboe
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