/g/ - syscall of the day: fadvise64 - Technology

Anonymous

syscall of the day: fadvise64 05/13/26(Wed)08:20:18 No.108813613

File: Tumblr_l_78011383013885.jpg (616 KB, 2048x1796)

syscall of the day: fadvise64 Anonymous 05/13/26(Wed)08:20:18 No.108813613 Archived

previous: >>108805935
#define __NR_fadvise64                221
https://man7.org/linux/man-pages/man2/fadvise64.2.html

tl;dr:
advise the kernel as to how you plan to access a file

this is kind of gross:
              The implementation may attempt to write back dirty pages in
              the specified region, but this is not guaranteed.  Any
              unwritten dirty pages will not be freed.  If the
              application wishes to ensure that dirty pages will be
              released, it should call fsync(2) or fdatasync(2) first.
either write them back, or else discard them all. don't tell me they may or may not get written back. the indeterminism is frightening

not something i've ever had occasion to use, but i can see where it would be useful

relevant resources:
man man
man syscalls
https://man7.org/linux/man-pages/
https://linux.die.net/man/
https://elixir.bootlin.com/linux/
https://elixir.bootlin.com/musl/
https://elixir.bootlin.com/glibc/

Anonymous
05/13/26(Wed)08:37:12 No.108813706

Anonymous 05/13/26(Wed)08:37:12 No.108813706

$500 say the nondeterminism (that's the word you managed to molest) is caused by caches not being retired to memory.

Anonymous
05/13/26(Wed)09:15:42 No.108813951

Anonymous 05/13/26(Wed)09:15:42 No.108813951

>>108813706
is that the word? it doesn't sound right
i know things can be nondeterministic, but i feel like with the -ism, it should have an in-
maybe i'm just overthinking it though

Anonymous
05/13/26(Wed)09:31:04 No.108814030

Anonymous 05/13/26(Wed)09:31:04 No.108814030

>>108813951
no, now that i think about it, i guess it should be nondeterminism
i was just being silly

Anonymous
05/13/26(Wed)12:09:39 No.108814956

Anonymous 05/13/26(Wed)12:09:39 No.108814956

I advise this thread to return to page 1.

Anonymous
05/13/26(Wed)12:28:43 No.108815088

Anonymous 05/13/26(Wed)12:28:43 No.108815088

>indeterminism is frightening
you don't use it for correctness issues, only for when you see a clear improvement in benchmarks by the kernel behaving less retardedly

Anonymous
05/13/26(Wed)17:21:34 No.108816911

Anonymous 05/13/26(Wed)17:21:34 No.108816911

>>108815088
i guess that's fair enough

Anonymous
05/13/26(Wed)17:45:36 No.108817066

Anonymous 05/13/26(Wed)17:45:36 No.108817066

>>108813613
>or until the end of the file if len is 0
god, this is exactly the convenience behaviour I wish many of the file syscalls had. I loathe the constant fstatting, and I usually don't even handle TOCTOU

Anonymous
05/13/26(Wed)23:36:07 No.108818760

Anonymous 05/13/26(Wed)23:36:07 No.108818760

>>108813613
POSIX permits the implementation to do anything or nothing at all in response to the advise functions, so you should never rely on them if there's some very specific behavior you want. They're purely for optimization hinting.

Anonymous
05/14/26(Thu)00:09:42 No.108818935

Anonymous 05/14/26(Thu)00:09:42 No.108818935

POSIX was a mistake. They should've just let UNIX die.