On Fri, Nov 05, 2021 at 02:34:58PM +0800, Yafang Shao wrote: > On Thu, Nov 4, 2021 at 9:37 AM Michał Mirosław <mirq-linux@xxxxxxxxxxxx> wrote: > > > > On Mon, Nov 01, 2021 at 06:04:08AM +0000, Yafang Shao wrote: > > > There're many truncated kthreads in the kernel, which may make trouble > > > for the user, for example, the user can't get detailed device > > > information from the task comm. > > > > > > This patchset tries to improve this problem fundamentally by extending > > > the task comm size from 16 to 24, which is a very simple way. > > [...] > > > > Hi, > > > > I've tried something like this a few years back. My attempt got mostly > > lost in the mailing lists, but I'm still carrying the patches in my > > tree [1]. My target was userspace thread names, and it turned out more > > involved than I had time for. > > > > [1] https://rere.qmqm.pl/git/?p=linux;a=commit;h=2c3814268caf2b1fee6d1a0b61fd1730ce135d4a > > and its parents > > > > Hi Michal, > > Thanks for the information. > > I have looked through your patches. It seems to contain six patches > now and can be divided into three parts per my understanding. > > 1. extend task comm len > This parts contains below 4 patches: > [prctl: prepare for bigger > TASK_COMM_LEN](https://rere.qmqm.pl/git/?p=linux;a=commit;h=cfd99db9cf911bb4d106889aeba1dfe89b6527d0) > [bluetooth: prepare for bigger > TASK_COMM_LEN](https://rere.qmqm.pl/git/?p=linux;a=commit;h=ba2805f5196865b81cc6fc938ea53af2c7c2c892) > [taskstats: prepare for bigger > TASK_COMM_LEN](https://rere.qmqm.pl/git/?p=linux;a=commit;h=4d29bfedc57b36607915a0171f4864ec504908ca) > [mm: make TASK_COMM_LEN > configurable](https://rere.qmqm.pl/git/?p=linux;a=commit;h=362acc35582445174589184c738c4d86ec7d174b) > > What kind of userspace issues makes you extend the task comm length ? > Why not just use /proc/[pid]/cmdline ? This was to enable longer thread names (as set by pthread_setname_np()). Currently its 16 bytes, and that's too short for e.g. Chrome's or Firefox'es threads. I believe that FreeBSD has 32-byte limit and so I expect that major portable code is already prepared for bigger thread names. > 2. A fix > Below patch: > [procfs: signal /proc/PID/comm write > truncation](https://rere.qmqm.pl/git/?p=linux;a=commit;h=d72027388d4d95db5438a7a574e0a03ae4b5d6d7) > > It seems this patch is incomplete ? I don't know what it means to do. Currently writes to /proc/PID/comm are silently truncated. This patch makes the write() call return the actual number of bytes actually written and on subsequent calls return -ENOSPC. glibc checks the length in pthread_setname_np() before write(), so the change is not currently relevant for it. I don't know/remember what other runtimes do, though. > 3. A feature provided for pthread_getname_np > Below patch: > [procfs: lseek(/proc/PID/comm, 0, > SEEK_END)](https://rere.qmqm.pl/git/?p=linux;a=commit;h=2c3814268caf2b1fee6d1a0b61fd1730ce135d4a) > > It seems this patch is useful. With this patch the userspace can > directly get the TASK_COMM_LEN through the API. This one I'm not really fond of because it abuses lseek() in that it doesn't move the write pointer. But in case of /proc files this normally would return EINVAL anyway. Best Regards Michał Mirosław
