How is /proc/self implemented in Linux

procprocess

I was tinkering around with the /proc filesystem in Linux, and I came across /proc/self, which is a symbolic link to the process directory of the current process. I would like to know how it is implemented. One solution would be to change that symlink on every context switch, but that's obviously very expensive as it involves a disk access.

Best Answer

http://lxr.linux.no/linux+v3.2.9/fs/proc/base.c#L2482 is the current implementation.

The proc filesystem is entirely virtual, and is implemented so the internal VFS readlink delegates to the right place for special symlinks. So, it calculates what self points to when it is read / traversed, not every context switch.

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Linux – /proc/self/maps – 3rd mapped piece of file

hi i had the same confuse as you, i had dig the internet and find this, i think this is the answer to your confuse too. link: https://stackoverflow.com/questions/33756119/relationship-between-vma-and-elf-segments

for shrot:

00400000-0040b000 r-xp 00000000 08:02 1186756             /usr/bin/cat
**use for store text code and const varibles**

0060a000-0060b000 r--p 0000a000 08:02 1186756             /usr/bin/cat
**use for GNU_RELRO relocated info**

0060b000-0060c000 rw-p 0000b000 08:02 1186756             /usr/bin/cat
use for bss data segment

hope this useful

Linux – ls -l /proc/self | increamental PID

Yes, that's the PID of ls.

POSIX defined ls as an external command, so anytime you run ls, the shell must create new process and run ls in that process.

To do that, the shell will call execve() system call:

$ strace ls -l /proc/self
execve("/bin/ls", ["ls", "-l", "/proc/self"], [/* 76 vars */]) = 0

You can see, after new process was created, /proc/self belongs to context of that process, so it was expanded to the PID of ls.

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Linux – /proc/self/maps – 3rd mapped piece of file

Linux – ls -l /proc/self | increamental PID

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