open_excl(3)

✨ NAME ✨

open_excl — open a file for exclusive writing 💅

okay so bestie, welcome to the open_excl(3) page from the Library Functions Manual. This function is lowkey iconic: it opens a file for exclusive writing, periodt.

🦋 SYNTAX 🦋

#include <libowfat/open.h>

int open_excl(const char *filename);

🌸 DESCRIPTION 🌸

So open_excl opens the file filename for writing and returns the file handle. But here's the vibe check: the file may not exist before the call to open_excl. Like, it has to be brand-new, bestie. The file will be created with mode 0600.

If there was an error creating the file, open_excl returns -1 and sets errno accordingly. So if you get -1, check errno, okay? 😭

Now the messy part: since open_excl relies on the O_EXCL flag to open, it does not work reliably over NFS (the NFS protocol is broken) and must be emulated using a lock file. The emulation tea: create a file with a unique file name and link(2) it to the lock file. Then stat the lock file and see if the link count is 2. That's it, that's the workaround. 🫶

👑 SEE ALSO 👑

• open(2)
• open_append(3)
• open_read(3)
• open_rw(3)
• open_trunc(3)
• open_write(3)
• openreadclose(3)
• readclose(3)
• readclose_append(3)

sign-off: this page is from the Library Functions Manual, titled open_excl(3), and there's no date on it. bye bestie 🫶✨