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RichFelker's profile
Rich Felker
Rich Felker
Rich Felker
@RichFelker

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Rich Felker

@RichFelker

Yeah, I do @musllibc, FOSS & infosec stuff. But now is not the time for a mostly-/only-tech Twitter feed.

musl-libc.org
Joined March 2014

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    1. Rich Felker‏ @RichFelker Apr 12

      TIL another awful thing about Linux procfs behavior; top-level /proc only reports processes (thread-groups) via getdents/readdir, but opening /proc/$tid where $tid is any thread id (not necessarily also a process id) succeeds.

      5 replies 8 retweets 29 likes
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    2. mork  👽‏ @corkmork Apr 12
      Replying to @RichFelker

      IIRC in earlier versions of Linux all tasks (processes, threads) were in /proc and when threads got moved (tasks without CLONE_VM?) the open behaviour was kept for backwards compatibility. At one point ps and top showed threads by default.

      1 reply 1 retweet 0 likes
      Rich Felker‏ @RichFelker Apr 12
      Replying to @corkmork

      Rich Felker Retweeted Rich Felker

      Yes I'm aware. See the other branch of this thread. Also it's CLONE_THREAD; you can use CLONE_VM without CLONE_THREAD, e.g. as vfork.https://twitter.com/RichFelker/status/984465290489749504 …

      Rich Felker added,

      Rich Felker @RichFelker
      My guess: this was some awful compromise with the historical zealots who didn't want Linux to support real threads at all because they thought the "processes sharing memory" model of LinuxThreads was sufficient...
      Show this thread
      1:56 PM - 12 Apr 2018
      4 replies 0 retweets 0 likes
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        2. mork  👽‏ @corkmork Apr 12
          Replying to @RichFelker

          Oh that’s right. Early on they only had CLONE_VM and no concept of tid. I think that is why CLONE_THREAD got added, so that proc and procps could differentiate processes from threads. I remember in the 2.4.x days a period where ps showed all threads as processes. Linus relented

          1 reply 0 retweets 1 like
        3. Rich Felker‏ @RichFelker Apr 12
          Replying to @corkmork

          Showing them in /proc was the least of the problems with this naive and bone-headed approach. Signal semantics, child process relationships, exec behavior, etc. were all wrong and could not be fixed just by emulating pthreads in userspace.

          0 replies 0 retweets 1 like
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        2. mork  👽‏ @corkmork Apr 12
          Replying to @RichFelker

          BSD ps would open /dev/men and because it was built as part of “make world” it had the same struct as the kernel. It was fast. Linux procps was slow because it had to open loads of files. top could be using the most cpu when you ran it. top at the top of top.

          1 reply 0 retweets 0 likes
        3. Rich Felker‏ @RichFelker Apr 12
          Replying to @corkmork

          Yep, I'm aware of the historical "let's make ps suid-root" awfulness of the BSDs. It was actually one of my turn-offs to BSD when first getting acquainted with Linux and FOSS. When was it finally fixed?

          3 replies 0 retweets 0 likes
        4. mork  👽‏ @corkmork Apr 12
          Replying to @RichFelker

          I don’t know. It dates back to the time when you could trust other nodes on the Internet, and services had no auth, before things like cleattext auth in pop3. You needed a local account for mail and uucp, sendmail and nntp all ran as root. sendmail had no authentication.

          0 replies 0 retweets 0 likes
        5. End of conversation
        1. mork  👽‏ @corkmork Apr 12
          Replying to @RichFelker

          This timeframe: http://lwn.net/2001/1108/a/proc-of-shit.php3 …

          0 replies 0 retweets 1 like
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        1. mork  👽‏ @corkmork Apr 12
          Replying to @RichFelker

          Linus would be saying Linux has “tasks” iirc

          0 replies 0 retweets 0 likes
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