4 ms·

Even those get most of their info from /proc and /sys rather than special syscalls

epcoa 3y ago
On the BSDs they sure don't, /proc (for its role referred to) and /sys are peculiar to Linux, /proc is not even mounted by default on FreeBSD, is deprecated and doesn't exist on OpenBSD. On OpenBSD/FreeBSD most of the info comes out with sysctl(3) or reading kernel memory directly.
- saagarjha 3y ago
  > reading kernel memory directly God I hope not
  - adrian_b 3y ago
    I do not know what the previous poster was talking about, but, while unrestricted access to kernel memory is of course unacceptable, a perfectly secure and useful means for the kernel to provide information to a user process is to map a page as read-only in the user address space, from where the user process could get the information without the overhead of a system call. For information of general interest such a special kernel page could be mapped as read-only in the address space of all user processes. Much of the information that is provided in the special file systems /proc and /sys could have been provided in some appropriate data structures in such read-only shared memory, for a faster access, by avoiding the overhead of file system calls and of file text parsing.
  - deleted 3y ago
    [deleted]
  - epcoa 3y ago
    https://man.freebsd.org/cgi/man.cgi?query=kvm&sektion=3&n=1 https://man.freebsd.org/cgi/man.cgi?query=kvm&sektion=3&n=1 The aforementioned tools use these interfaces. Emphasis on most of the sundry information for the live kernel now comes from sysctl, I note the (root only) mem/kmem interface for completeness and rare utilities (eg btsockstat) use it. Going way back, this is how it all used to work, the more structured interfaces were a 90s thing. https://github.com/v7unix/v7unix/blob/master/v7/usr/src/cmd/ps.c https://github.com/v7unix/v7unix/blob/master/v7/usr/src/cmd/... Even early Linux used kmem for ps. Not ideal https://cdn.kernel.org/pub/linux/kernel/Historic/old-versions/RELNOTES-0.97 https://cdn.kernel.org/pub/linux/kernel/Historic/old-version... Also why the package is still called procps, for a while it coexisted with kmem-ps.

On the BSDs they sure don't, /proc (for its role referred to) and /sys are peculiar to Linux, /proc is not even mounted by default on FreeBSD, is deprecated and doesn't exist on OpenBSD. On OpenBSD/FreeBSD most of the info comes out with sysctl(3) or reading kernel memory directly.

saagarjha 3y ago
> reading kernel memory directly God I hope not
- adrian_b 3y ago
  I do not know what the previous poster was talking about, but, while unrestricted access to kernel memory is of course unacceptable, a perfectly secure and useful means for the kernel to provide information to a user process is to map a page as read-only in the user address space, from where the user process could get the information without the overhead of a system call. For information of general interest such a special kernel page could be mapped as read-only in the address space of all user processes. Much of the information that is provided in the special file systems /proc and /sys could have been provided in some appropriate data structures in such read-only shared memory, for a faster access, by avoiding the overhead of file system calls and of file text parsing.
- deleted 3y ago
  [deleted]
- epcoa 3y ago
  https://man.freebsd.org/cgi/man.cgi?query=kvm&sektion=3&n=1 https://man.freebsd.org/cgi/man.cgi?query=kvm&sektion=3&n=1 The aforementioned tools use these interfaces. Emphasis on most of the sundry information for the live kernel now comes from sysctl, I note the (root only) mem/kmem interface for completeness and rare utilities (eg btsockstat) use it. Going way back, this is how it all used to work, the more structured interfaces were a 90s thing. https://github.com/v7unix/v7unix/blob/master/v7/usr/src/cmd/ps.c https://github.com/v7unix/v7unix/blob/master/v7/usr/src/cmd/... Even early Linux used kmem for ps. Not ideal https://cdn.kernel.org/pub/linux/kernel/Historic/old-versions/RELNOTES-0.97 https://cdn.kernel.org/pub/linux/kernel/Historic/old-version... Also why the package is still called procps, for a while it coexisted with kmem-ps.