LC_MMAPFILE(3)

💖 LC_MMAPFILE(3) 💖

okay bestie, welcome to Librecast's little cutie of a function — meet lc_mmapfile, the girl who maps (or unmaps!) files or devices straight into memory. she lives in the Librecast Programmer's Manual, and yes she's part of the Librecast library — that's liblibrecast, linked with -llibrecast. slay. ✨

🌸 LIBRARY 🌸

Librecast library (liblibrecast, -llibrecast) 🫶

✨ SYNOPSIS ✨

#include <librecast/sync.h>

void *lc_mmapfile(const char *pathname, size_t *len, int prot, int flags,
                  off_t offset, struct stat *sb);

Compile and link with -llibrecast. no cap, that's the whole vibe 💅

🦋 DESCRIPTION 🦋

so lc_mmapfile() is literally just a convenience wrapper for mmap(2) — it open(2)s and maps a file in a single call, because who has time for two calls when one will do. if you want the full lore, go read mmap(2).

here's the tea, ok:

• if prot has the PROT_WRITE flag set, then pathname gets open(2)'ed with the O_RDWR and O_CREAT flags set — so the file is created and opened read-write 💖
• otherwise it's opened O_RDONLY 🌸
• wanna set the mode for the file being created? set st_mode in sb when you call lc_mmapfile(). that's it, that's the trick ✨

and about len:

• if len points to a value greater than zero, then ftruncate(2) is called to truncate the file to that specified length ✂️
• otherwise, the variable len points to is set to the size of the file 👑

when you're done, the file can be unmapped and the memory freed by calling munmap(3). clean up after yourself, bestie 🧹

🔥 RETURN VALUE 🔥

on success, lc_mmapfile() returns a pointer to the mapped area. iconic. 👑

on error, the value MAP_FAILED (that is, (void*)-1) is returned, and errno is set to indicate the error. it's giving sad girl era 😭

💀 ERRORS 💀

• ENODATA — File is zero length. yeah. nothing there. empty. the void. 🫠

See also open(2), mmap(2), fstat(2), and ftruncate(2).

🌈 SEE ALSO 🌈

• mmap(2)
• msync(2)
• munmap(2)
• open(2)
• fstat(2)
• ftruncate(2)

💜 that's the whole page bestie, go forth and map some memory. iykyk.

LIBRECAST · 2023-07-24 · LC_MMAPFILE(3) — mwah, bye, love u, see u in the group chat 💅🎀🦋