|
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
{
} File;
typedef struct Tree
{
} Tree;
Tree* alloctree(char *uid, char *gid, ulong mode,
void freetree(Tree *tree)
File* createfile(File *dir, char *name, char *uid,
int removefile(File *file)
void closefile(File *file)
File* walkfile(File *dir, char *path)
Readdir* opendirfile(File *dir)
long readdirfile(Readdir *rdir, char *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 inherited from the directory. Mode and the permissions
of dir are used to calculate the permission bits for the file
as described in open(9p). It is permissible
for name to be a slash-separated path rather than a single 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(3)) 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 reference.
Directories may be read, yielding a directory entry structure
(see stat(9p)) 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 implementation
to provide more complex groups.
|
EXAMPLE
| |
The following code correctly handles references when elementwise
walking 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)
nf = createfile(f, "foo", "nls", 0666, nil);
closefile(f);
return nf;
|
|
SOURCE
SEE ALSO
BUGS
| |
The reference counting is cumbersome.
|
|
|
