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UKFS(3) NetBSD Library Functions Manual UKFS(3)
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ukfs -- user kernel file system library interface
ukfs Library (libukfs, -lukfs)
The ukfs library provides direct access to file systems without having to
specially mount a file system. Therefore, accessing a file system
through ukfs requires no special kernel support apart from standard POSIX
functionality. As ukfs is built upon rump(3) kernels, all kernel file
systems which are supported by rump kernels are available. It allows to
write utilities for accessing file systems without having to duplicate
file system internals knowledge already present in kernel file system
ukfs provides a high-level pathname based interface for accessing file
systems. If a lower level interface it desired, rump(3) kernels should
be used directly. However, much like system calls, the interfaces of
ukfs are self-contained and require no tracking and release of resources.
The only exception is the file system handle struct ukfs which should be
released after use.
ukfs_modload(const char *fname)
ukfs_modload_dir(const char *dirname)
ukfs_vfstypes(char *buf, size_t buflen)
struct ukfs *
ukfs_mount(const char *vfsname, const char *devpath, const char
*mountpath, int mntflags, void *arg, size_t alen)
struct ukfs *
ukfs_mount_disk(const char *vfsname, const char *devpath, int partition,
const char *mountpath, int mntflags, void *arg, size_t alen)
ukfs_release(struct ukfs *ukfs, int flags)
ukfs_init() initializes the library and must be called once per process
ukfs_modload() is used at runtime to dynamically load a library which
contains a file system module. For this to succeed, the rump(3) kernel
and the module targetted must be compiled with compatible kernel versions
and the application must be dynamically linked. Additionally, since this
routine does not handle dependencies, all the dependencies of the library
must be loaded beforehand. The routine returns -1 for fatal error, 0 for
dependency failure and 1 for success.
ukfs_modload_dir() loads all rump(3) kernel file system components in
directory dirname. It looks for libraries which begin with librumpfs_
and end in .so. The routine tries to handle dependencies by retrying to
load libraries which failed due to dependencies. ukfs_modload_dir()
returns the number of vfs modules loaded or sets errno and returns -1 in
case of a fatal error in directory searching. In case a fatal error
occurs after some modules have already been loaded, the number of loaded
module is returned. Fatal errors in loading the modules themselves are
ignored and ukfs_modload() should be used directly if finegrained error
reporting is desired.
It should be noted that the above routines affect the whole process, not
just a specific instance of ukfs. It is preferable to call them from
only one thread, as the underlying dynamic library interfaces may not be
ukfs_vfstypes() queries the available file system types and returns a
nul-terminated list of types separated by spaces in buf. The format of
the list is equivalent to the one returned by sysctl(3) on the name
vfs.generic.fstypes. The function returns the length of the string with-
out the trailing nul or -1 for error. Notably, the return value 0 means
there are no file systems available. If there is not enough room in the
caller's buffer for all file system types, as many as fit will be
ukfs_mount() initializes a file system image. The handle resulting from
the operation is passed to all other routines and identifies the instance
of the mount analoguous to what a pathname specifies in a normally
mounted file system. The parameters are the following:
Name of the file system to be used, e.g. MOUNT_FFS.
Path of file system image. It can be either a regular file,
device or, if the file system does not support the concept of
a device, an abitrary string, e.g. network address.
Path where the file system is mounted to. This parameter is
used only by the file system being mounted. Most of the time
UKFS_DEFAULTMP is the correct path.
Flags as passed to the mount(2) system call, for example
MNT_RDONLY. In addition to generic parameters, file system
specific parameters such as MNT_LOG (ffs) may be passed here.
arg File system private argument structure. This is passed
directly to the file system. It must match what vfsname
Size of said structure.
The ukfs_mount_disk() function must be used to mount disk-based file sys-
tems. It takes the same arguments as ukfs_mount(), except for an addi-
tional argument signifying the partition number. If the image devpath
contains a disklabel, this value specifies the number of the partition
within the image used as the file system backend. If devpath does not
contain a disklabel, the value UKFS_PARTITION_NONE must be used to signal
that the file system backend is the entire image.
ukfs_release() unmounts the file system and releases the resources asso-
ciated with ukfs. The return value signals the return value of the
unmount operation. If non-zero, ukfs will continue to remain valid. The
possible values for flags are:
UKFS_RELFLAG_NOUNMOUNT Do not unmount file system, just release
ukfs handle. Release always succeeds.
UKFS_RELFLAG_FORCE Forcefully unmount the file system. This
means that any busy nodes (due to e.g.
ukfs_chdir()) will be ignored. Release
ukfs_chdir(struct ukfs *ukfs, const char *path)
ukfs_getdents(struct ukfs *ukfs, const char *dirname, off_t *off, uint8_t
*buf, size_t bufsize)
ukfs_read(struct ukfs *ukfs, const char *filename, off_t off, uint8_t
*buf, size_t bufsize)
ukfs_write(struct ukfs *ukfs, const char *filename, off_t off, uint8_t
*buf, size_t bufsize)
ukfs_create(struct ukfs *ukfs, const char *filename, mode_t mode)
ukfs_mknod(struct ukfs *ukfs, const char *path, mode_t mode, dev_t dev)
ukfs_mkfifo(struct ukfs *ukfs, const char *path, mode_t mode)
ukfs_mkdir(struct ukfs *ukfs, const char *filename, mode_t mode)
ukfs_remove(struct ukfs *ukfs, const char *filename)
ukfs_rmdir(struct ukfs *ukfs, const char *filename)
ukfs_link(struct ukfs *ukfs, const char *filename, const char *f_create)
ukfs_symlink(struct ukfs *ukfs, const char *filename, const char
ukfs_readlink(struct ukfs *ukfs, const char *filename, char *linkbuf,
ukfs_rename(struct ukfs *ukfs, const char *from, const char *to)
ukfs_stat(struct ukfs *ukfs, const char *filename, struct stat
ukfs_lstat(struct ukfs *ukfs, const char *filename, struct stat
ukfs_chmod(struct ukfs *ukfs, const char *filename, mode_t mode)
ukfs_lchmod(struct ukfs *ukfs, const char *filename, mode_t mode)
ukfs_chown(struct ukfs *ukfs, const char *filename, uid_t uid, gid_t gid)
ukfs_lchown(struct ukfs *ukfs, const char *filename, uid_t uid, gid_t
ukfs_chflags(struct ukfs *ukfs, const char *filename, u_long flags)
ukfs_lchflags(struct ukfs *ukfs, const char *filename, u_long flags)
ukfs_utimes(struct ukfs *ukfs, const char *filename, const struct timeval
ukfs_lutimes(struct ukfs *ukfs, const char *filename, const struct
The above routines operate like their system call counterparts and the
system call manual pages without the ukfs_ prefix should be referred to
for further information on the parameters.
The only call which modifies ukfs state is ukfs_chdir(). It works like
chdir(2) in the sense that it affects the interpretation of relative
paths. If succesful, all relative pathnames will be resolved starting
from the current directory. Currently the call affects all accesses to
that particular ukfs, but it might be later changed to be thread private.
ukfs_util_builddirs(struct ukfs *ukfs, const char *pathname, mode_t mode)
Builds a directory hierarchy. Unlike mkdir, the pathname argument may
contain multiple levels of hierarchy. It is not considered an error if
any of the directories specified exist already.
ukfs first appeared in NetBSD 5.0.
Antti Kantee <firstname.lastname@example.org>
ukfs was an early attempt at an interface for kernel file systems running
NetBSD 9.1 March 12, 2018 NetBSD 9.1