9PFILE(2)9PFILE(2)NAME
Tree, alloctree, freetree, File, createfile, closefile, removefile,
walkfile, opendirfile, readdirfile, closedirfile, hasperm - in-memory
file hierarchy
SYNOPSIS
#include <u.h>
#include <libc.h>
#include <fcall.h>
#include <thread.h>
#include <9p.h>
typedef struct File
{
Ref;
Dir;
void*aux;
...
} File;
typedef struct Tree
{
File *root;
...
} Tree;
Tree* alloctree(char *uid, char *gid, ulong mode,
void (*destroy)(File*))
void freetree(Tree *tree)
File* createfile(File *dir, char *name, char *uid,
ulong mode, void *aux)
int removefile(File *file)
void closefile(File *file)
File* walkfile(File *dir, char *path)
Readdir* opendirfile(File *dir)
long readdirfile(Readdir *rdir, uchar *buf, long n)
void closedirfile(Readdir *rdir)
int hasperm(File *file, char *uid, int p)
DESCRIPTION
Files and Trees provide an in-memory file hierarchy intended for use in
9P file servers.
Alloctree creates a new tree of files, and freetree destroys it. The
root of the tree (also the root element in the structure) will have
mode mode and be owned by user uid and group gid. Destroy is used when
freeing File structures and is described later.
Files (including directories) other than the root are created using
createfile, which attempts to create a file named name in the directory
dir. If created, the file will have owner uid and have a group inher‐
ited from the directory. Mode and the permissions of dir are used to
calculate the permission bits for the file as described in open(5). It
is permissible for name to be a slash-separated path rather than a sin‐
gle element.
Removefile removes a file from the file tree. The file will not be
freed until the last reference to it has been removed. Directories may
only be removed when empty. Removefile returns zero on success, -1 on
error. It is correct to consider removefile to be closefile with the
side effect of removing the file when possible.
Walkfile evaluates path relative to the directory dir, returning the
resulting file, or zero if the named file or any intermediate element
does not exist.
The File structure's aux pointer may be used by the client for per-File
storage. Files are reference-counted: if not zero, destroy (specified
in the call to alloctree) will be called for each file when its last
reference is removed or when the tree is freed. Destroy should take
care of any necessary cleanup related to aux. When creating new file
references by copying pointers, call incref (see lock(2)) to update the
reference count. To note the removal of a reference to a file, call
closefile. Createfile and walkfile return new references. Removefile,
closefile, and walkfile (but not createfile) consume the passed refer‐
ence.
Directories may be read, yielding a directory entry structure (see
stat(5)) for each file in the directory. In order to allow concurrent
reading of directories, clients must obtain a Readdir structure by
calling opendirfile on a directory. Subsequent calls to readdirfile
will each yield an integral number of machine-independent stat buffers,
until end of directory. When finished, call closedirfile to free the
Readdir.
Hasperm does simplistic permission checking; it assumes only one-user
groups named by uid and returns non-zero if uid has permission p (a
bitwise-or of AREAD, AWRITE and AEXEC) according to file->mode. 9P
servers written using File trees will do standard permission checks
automatically; hasperm may be called explicitly to do additional
checks. A 9P server may link against a different hasperm implementa‐
tion to provide more complex groups.
EXAMPLE
The following code correctly handles references when elementwise walk‐
ing a path and creating a file.
f = tree->root;
incref(f);
for(i=0; i<n && f!=nil; i++)
f = walkfile(f, elem[i]);
if(f == nil)
return nil;
nf = createfile(f, "foo", "nls", 0666, nil);
closefile(f);
return nf;
SOURCE
/sys/src/lib9p/file.c
SEE ALSO9p(2)BUGS
The reference counting is cumbersome.
9PFILE(2)
