LIBNFS is a client library for accessing NFS shares over a network.
LIBNFS offers three different APIs, for different use :
1, RAW : A fully async low level RPC library for NFS protocols
This API is described in include/libnfs-raw.h
it offers a fully async interface to raw XDR encoded blobs.
This API provides very flexible and precise control of the RPC issued.
examples/nfsclient-raw.c provides examples on how to use the raw API
2, NFS ASYNC : A fully asynchronous library for high level vfs functions
This API is described by the *_async() functions in include/libnfs.h.
This API provides a fully async access to posix vfs like functions such as
stat(), read(), ...
examples/nfsclient-async.c provides examples on how to use this API
3, NFS SYNC : A synchronous library for high level vfs functions
This API is described by the *_sync() functions in include/libnfs.h.
This API provides access to posix vfs like functions such as
stat(), read(), ...
examples/nfsclient-sync.c provides examples on how to use this API
NFSv4:
======
NFSv3 is the default but NFSv4 can be selected either by using the URL argument
version=4 or programatically calling nfs_set_version(nfs, NFS_V4) before
connecting to the server/share.
SERVER SUPPORT:
===============
Libnfs supports building RPC servers.
Examples/portmapper-server.c is a small "portmapper" example written using
libnfs.
URL-FORMAT:
===========
Libnfs uses RFC2224 style URLs extended with some minor libnfs extensions.
The basic syntax of these URLs is :
nfs://<server|ipv4|ipv6>/path[?arg=val[&arg=val]*]
Arguments supported by libnfs are :
tcp-syncnt=<int> : Number of SYNs to send during the session establish
before failing setting up the tcp connection to the
server.
uid=<int> : UID value to use when talking to the server.
default it 65534 on Windows and getuid() on unixen.
gid=<int> : GID value to use when talking to the server.
default it 65534 on Windows and getgid() on unixen.
readahead=<int> : Enable readahead for files and set the maximum amount
of readahead to <int> bytes.
auto-traverse-mounts=<0|1>
: Should libnfs try to traverse across nested mounts
automatically or not. Default is 1 == enabled.
dircache=<0|1> : Disable/enable directory caching. Enabled by default.
autoreconnect=<-1|0|>=1>
: Control the auto-reconnect behaviour to the NFS session.
-1 : Try to reconnect forever on session failures.
Just like normal NFS clients do.
0 : Disable auto-reconnect completely and immediately
return a failure to the application.
>=1 : Retry to connect back to the server this many
times before failing and returing an error back
to the application.
if=<interface> : Interface name (e.g., eth1) to bind; requires `root`
version=<3|4> : NFS Version. Default is 3.
nfsport=<port> : Use this port for NFS instead of using the portmapper.
mountport=<port> : Use this port for the MOUNT protocol instead of
using portmapper. This argument is ignored for NFSv4
as it does not use the MOUNT protocol.
Auto_traverse_mounts
====================
Normally in NFSv3 if a server has nested exports, for example if it would
export both /data and /data/tmp then a client would need to mount
both these exports as well.
The reason is because the NFSv3 protocol does not allow a client request
to return data for an object in a different filesystem/mount.
(legacy, but it is what it is. One reason for this restriction is to
guarantee that inodes are unique across the mounted system.)
This option, when enabled, will make libnfs perform all these mounts
internally for you. This means that one libnfs mount may now have files
with duplicate inode values so if you cache files based on inode
make sure you cache files based on BOTH st.st_ino and st.st_dev.
ROOT vs NON-ROOT
================
When running as root, libnfs tries to allocate a system port for its connection
to the NFS server. When running as non-root it will use a normal
ephemeral port.
Many NFS servers default to a mode where they do not allow non-system
ports from connecting.
These servers require you use the "insecure" export option in /etc/exports
in order to allow libnfs clients to be able to connect.
On Linux we can get around this restriction by setting the NET_BIND_SERVICE
capability for the application binary.
This is set up by running
sudo setcap 'cap_net_bind_service=+ep' /path/to/executable
This capability allows the binary to use systems ports like this even when
not running as root. Thus if you set this capability for your application
you no longer need to edit the export on the NFS server to set "insecure".
I do not know what equivalent "capability" support is available on other
platforms. Please drop me an email if your os of choice has something similar
and I can add it to the README.
DOCUMENTATION
=============
libnfs sources ship with prebuilt manpage(s) in the doc directory.
If you change the manpage sources you need to manually regenerate the new
manpages by running
cd doc
make doc
PLATFORM support
=================
This is a truly multiplatform library.
Linux: - tested with Ubuntu 10.04 - should work with others as well
Cygwin: - tested under 64bit win2k8.
MacOSX: - tested with SDK 10.4 (under Snow Leopard) - should also work with later SDKs and 64Bit
iOS: - tested with iOS SDK 4.2 - running on iOS 4.3.x
FreeBSD:- tested with 8.2
Solaris
Windows:- tested on Windows 7 64 and Windows XP 32 using Visual Studio 10 (see README.win32.txt for build instructions)
- tested on Windows 7 64 using MingW on Linux to cross-compile (Debian and Ubuntu tested)
Android:- tested with NDK r10e - running on Android 4.4 (should work starting from 2.3.3)
AROS: - Build with 'make -f aros/Makefile.AROS'
LD_PRELOAD
==========
examples/ld_nfs.c contains a LD_PRELOADable module that can be used to make
several standard utilities nfs aware.
It is still very incomplete but can be used for basic things such as cat and cp.
Patches to add more coverage is welcome.
Compile with :
gcc -fPIC -shared -o ld_nfs.so examples/ld_nfs.c -ldl -lnfs
Then try things like
LD_NFS_DEBUG=9 LD_PRELOAD=./ld_nfs.so cat nfs://127.0.0.1/data/tmp/foo123
LD_NFS_DEBUG=9 LD_PRELOAD=./ld_nfs.so cp nfs://127.0.0.1/data/tmp/foo123 nfs://127.0.0.1/data/tmp/foo123.copy
LD_NFS_UID and LD_NFS_GID can be used to fake the uid andthe gid in the nfs context.
This can be useful on "insecure" enabled NFS share to make the server trust you as a root.
You can try to run as a normal user things like :
LD_NFS_DEBUG=9 LD_NFS_UID=0 LD_NFS_GID=0 LD_PRELOAD=./ld_nfs.so chown root:root nfs://127.0.0.1/data/tmp/foo123
This is just a toy preload module. Don't open bugs if it does not work. Send
patches to make it better instead.
RELEASE TARBALLS
================
Release tarballs are available at
https://sites.google.com/site/libnfstarballs/li
MAILING LIST
============
A libnfs mailing list is available at http://groups.google.com/group/libnfs
Announcements of new versions of libnfs will be posted to this list.