Re: develoment workflow: how to avoid duplicate work ?
> > It's not duplication, it's increment/decrement of a counter. > > > > Look for functions with 'get' and 'put' in their names. > > AFAICT counter is f_count in struct file, updated by fget and fput. Yes, this is the counter I was speaking about. But to me the only way to increment/decrement this counter was either to duplicate an existing reference using dup/dup2, or to fork the process. This was wrong, and I'm glad I learned that. FTR: After taking a look at the kernel code, the ioctl syscall is implemented in ksys_ioctl[0], which calls fdget/fdput to get the struct fd, incrementing and decrementing the count. Thanks your help ! > > I haven't looked at the code - there's an outside chance that the driver > > isn't doing reference counting correctly. > > pi433 driver does not mess with struct file too much so I guess it should > be safe :) I'll take a closer look at the TODO and come back later with a patch. If there's nothing to do I'll remove it, otherwise I'll fix it. Cheers, Hugo [0] https://elixir.bootlin.com/linux/latest/source/fs/ioctl.c#L692 -- Hugo Lefeuvre (hle)|www.owl.eu.com 4096/ 9C4F C8BF A4B0 8FC5 48EB 56B8 1962 765B B9A8 BACA ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: a Linux device driver
On Tue, 05 Jun 2018 13:51:54 -0700, Abu Rasheda said: > right now, I am in a mood to write a driver, not testing :) Can you, in a few sentences, explain why the Linux community wants a driver written by somebody who wanted to write a driver but didn't want to do the testing needed to ensure it doesn't blow up the card, or burn out the USB hub, or turn your dog green? pgpMiYy__eeoh.pgp Description: PGP signature ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: a Linux device driver
On Tue, Jun 5, 2018 at 1:51 AM, Ozgur Kara wrote: > > > 05.06.2018, 08:57, "valdis.kletni...@vt.edu" : > > On Mon, 04 Jun 2018 15:49:37 -0700, Abu Rasheda said: > > > >> Any recommendations what device driver is missing and open source > >> community could benefit from a new driver or enhance some existing > driver? > > > > Short answer: One that you have the hardware for so you can actually > test your code. > > Nobody wants to see a driver for a Frobnozz 9000 graphics card written > by somebody who > > doesn't have access to a Frobmozz 9000 card for testing. > > > wondering which hardware is missing a driver, I can try yo buy/acquire the hardware > Long answer: https://lists.kernelnewbies.org/pipermail/kernelnewbies/ > 2017-April/017765.html > right now, I am in a mood to write a driver, not testing :) > in addition, > > You can browse the staging directory in the kernel source and check. > > will do thanks Regards > > Ozgur > > > > > ___ > > Kernelnewbies mailing list > > Kernelnewbies@kernelnewbies.org > > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: develoment workflow: how to avoid duplicate work ?
On Tue, 05 Jun 2018 10:20:16 -0400, Hugo Lefeuvre said: > Thanks. I think I'll have to read the source code to fully understand > what happens. Do you know what piece of code handles this reference > duplication ? It's not duplication, it's increment/decrement of a counter. Look for functions with 'get' and 'put' in their names. > As a conclusion we can assume that ioctl and release never run > concurrently, and as such the lock introduced in my patch is useless. Well, they *shouldn't* do so. What the code actually does, however > Concerning the TODO at line 876, I think I've misunderstood it. I'll > think a bit more about it and come back with an updated patch later. I haven't looked at the code - there's an outside chance that the driver isn't doing reference counting correctly. pgpKD7Q7Lgaa1.pgp Description: PGP signature ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: develoment workflow: how to avoid duplicate work ?
> > Do you mean that the ioctl/read/write call increments the reference > > count in this case ? It would mean that these syscalls aren't really > > using passed FD but instead create duplicates to make sure the open > > file description won't be freed during their execution, right ? > > One file descriptor is passed around, and each syscall or other code that > needs > to protect it from evaporating out from under it takes a reference. Thanks. I think I'll have to read the source code to fully understand what happens. Do you know what piece of code handles this reference duplication ? As a conclusion we can assume that ioctl and release never run concurrently, and as such the lock introduced in my patch is useless. Concerning the TODO at line 876, I think I've misunderstood it. I'll think a bit more about it and come back with an updated patch later. Thanks ! Cheers, Hugo -- Hugo Lefeuvre (hle)|www.owl.eu.com 4096/ 9C4F C8BF A4B0 8FC5 48EB 56B8 1962 765B B9A8 BACA signature.asc Description: PGP signature ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: a Linux device driver
05.06.2018, 08:57, "valdis.kletni...@vt.edu" : > On Mon, 04 Jun 2018 15:49:37 -0700, Abu Rasheda said: > >> Any recommendations what device driver is missing and open source >> community could benefit from a new driver or enhance some existing driver? > > Short answer: One that you have the hardware for so you can actually test > your code. > Nobody wants to see a driver for a Frobnozz 9000 graphics card written by > somebody who > doesn't have access to a Frobmozz 9000 card for testing. > > Long answer: > https://lists.kernelnewbies.org/pipermail/kernelnewbies/2017-April/017765.html in addition, You can browse the staging directory in the kernel source and check. Regards Ozgur > > ___ > Kernelnewbies mailing list > Kernelnewbies@kernelnewbies.org > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
