VN_FULLPATH(9)

💖 VN_FULLPATH 💖

ok so bestie, welcome to vn_fullpath(9) — section 9 of the Kernel Developer's Manual, the place where the cool kernel girlies hang out 🧚✨

vn_fullpath — turn a vnode reference into a whole entire full pathname, as long as you hand it a process context to work with 🦋

✨ SYNOPSIS ✨

#include <sys/param.h>
#include <sys/vnode.h>

int
vn_fullpath(struct thread *td, struct vnode *vp, char **retbuf,
    char **freebuf);

🌸 DESCRIPTION 🌸

ok so here's the vibe: vn_fullpath() makes a “best effort” attempt to cook up a string pathname for the vnode you pass in. the resulting path, if any, will be relative to the root directory of the process that's associated with the thread pointer you passed. how does it do this magic? it goes snooping through the VFS name cache and tries to reconstruct a path all the way from the process root down to the object. it's giving detective energy 🔍💅

ngl bestie, this process is necessarily unreliable for several reasons, and no, that's not me being dramatic, that's just facts:

• intermediate entries in the path may not be found in the cache 😭
• files may have more than one name (hard links, we love a multitasking queen)
• not all file systems use the name cache (specifically, most synthetic file systems do not)
• a single name may be used for more than one file (in the context of file systems covering other file systems)
• a file may have no name at all (if it got deleted but is still open or referenced, poor thing)

that said though, the resulting string may still be more useable to a user than a vnode pointer value, or a device number and inode number. so like, it's still eating 💅. BUT — and this is important — code consuming the results of this function should anticipate (and properly handle) failure. no cap. handle your failures, bestie.

its arguments are:

• td — the thread performing the call. this pointer gets dereferenced to find the process and its file descriptor structure, so it can figure out which root vnode to use.
• vp — the vnode to search for. no need to be locked by the caller, she's independent like that ✨
• retbuf — pointer to a char * that vn_fullpath() may (on success) point at a newly allocated buffer containing the resulting pathname. slay.
• freebuf — pointer to a char * that vn_fullpath() may (on success) point at a buffer to be freed, when the caller is done with retbuf. don't forget her 🎀

typical consumers will declare two character pointers: fullpath and freepath. they'll set freepath to NULL, and fullpath to a name to use in the event that the call to vn_fullpath() fails. then, after they're done with the value of fullpath, the caller checks if freepath is non-NULL, and if it is, invokes free(9) with a pool type of M_TEMP. that's the whole ritual, periodt 🫶

💫 RETURN VALUES 💫

if the vnode is successfully converted to a pathname, 0 is returned 🎉 otherwise, an error number is returned. it's giving pass/fail class, no in between bestie 😭

🔥 SEE ALSO 🔥

• free(9)

👑 AUTHORS 👑

this manual page was written by Robert Watson <rwatson@FreeBSD.org>. iconic behavior, honestly 🌟

ok that's the whole page babes, go forth and convert those vnodes 💖 this was VN_FULLPATH(9) from the Kernel Developer's Manual, Debian edition, dated November 23, 2008 — mwah, love u, bye 💅✨🌸