freebsd-skq/share/man/man9/vn_fullpath.9

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.Dd November 23, 2008
.Dt VN_FULLPATH 9
.Os
.Sh NAME
.Nm vn_fullpath
.Nd "convert a vnode reference to a full pathname, given a process context"
.Sh SYNOPSIS
.In sys/param.h
.In sys/vnode.h
.Ft int
.Fo vn_fullpath
.Fa "struct thread *td" "struct vnode *vp" "char **retbuf" "char **freebuf"
.Fc
.Sh DESCRIPTION
The
.Fn vn_fullpath
function makes a
.Dq "best effort"
attempt to generate a string pathname for
the passed vnode; the resulting path, if any, will be relative to
the root directory of the process associated with the passed thread pointer.
The
.Fn vn_fullpath
function
is implemented by inspecting the VFS name cache, and attempting to
reconstruct a path from the process root to the object.
.Pp
This process is necessarily unreliable for several reasons: intermediate
entries in the path may not be found in the cache; files may have more
than one name (hard links), 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 (if deleted but still
open or referenced).
However, the resulting string may still be more useable to a user than
a vnode pointer value, or a device number and inode number.
Code consuming the results of this function should anticipate (and
properly handle) failure.
.Pp
Its arguments are:
.Bl -tag -width ".Fa freebuf"
.It Fa td
The thread performing the call; this pointer will be dereferenced to find
the process and its file descriptor structure, in order to identify the
root vnode to use.
.It Fa vp
The vnode to search for.  No need to be locked by the caller.
.It Fa retbuf
Pointer to a
.Vt "char *"
that
.Fn vn_fullpath
may (on success) point at a newly
allocated buffer containing the resulting pathname.
.It Fa freebuf
Pointer to a
.Vt "char *"
that
.Fn vn_fullpath
may (on success) point at a buffer
to be freed, when the caller is done with
.Fa retbuf .
.El
.Pp
Typical consumers will declare two character pointers:
.Va fullpath
and
.Va freepath ;
they will set
.Va freepath
to
.Dv NULL ,
and
.Va fullpath
to a name to use
in the event that the call to
.Fn vn_fullpath
fails.
After done with the value of
.Va fullpath ,
the caller will check if
.Va freepath
is
.Pf non- Dv NULL ,
and if so, invoke
.Xr free 9
with a pool type of
.Dv M_TEMP .
.Sh RETURN VALUES
If the vnode is successfully converted to a pathname, 0 is returned;
otherwise, an error number is returned.
.Sh SEE ALSO
.Xr free 9
.Sh AUTHORS
This manual page was written by
.An Robert Watson Aq rwatson@FreeBSD.org .