--- Read this first This version 2 of the libnfs API. It is not compatible with the earlier API. All rpc_<protocol><function>async() functions have been changed to rpc<protocol><dunction>_task(). The _task() functions return a struct rpc_pdu * which can later be used to cancel an inflight command.

nfs_[]read and nfs_[p]write functions have new signatures. Pay attention to any compiler warnings when compiling against this new API.

The symbol LIBNFS_API_V2 can be used to identify that the library uses the new API.

This version of the library supports zero-copy read and write for NFS v3/4

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://[<username>@]<server|ipv4|ipv6>[:<port>]/path[?arg=val[&arg=val]*]

Special characters in 'path' are escaped using %-hex-hex syntax.

For example '?' must be escaped if it occurs in a path as '?' is also used to separate the path from the optional list of url arguments.

Example: nfs://127.0.0.1/my?path/?version=4 must be escaped as nfs://127.0.0.1/my%3Fpath/?version=4

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. debug=<int> : Debug level used by libnfs. Default is 0 which is quiet. Higher values increase verbosity. timeo=<int> : The time in deciseconds (tenths of a second) libnfs client will wait for a response before it retries an RPC request. Default value of 'timeo' is 600, i.e., 60 seconds. Values less than 100, i.e., 10 seconds, are not allowed. retrans=<int> : After 'retrans' failed retries libnfs will generate a "server not responding" message and then attempt further recovery action. If no successful RPC response has been received over the connection for the last 'timeo' period, then the connection would be terminated and all queued RPCs will be retried over the new connection. If other RPC responses are being received then it means connection is fine and this is likely a problem with this specific RPC, in that case it'll simply keep retrying the RPC for ever at 'timeo' interval. This mimics the 'hard' mount behaviour of NFS clients. If 'retrans' is 0, then RPC is not retried on timeout but instead failed with RPC_STATUS_TIMEOUT. This will roughly mimic the 'soft' mount behaviour of NFS clients. Default value of 'retrans' is 2. sec=<krb5|krb5i|krb5p> : Specify the security mode. xprtsec=<none|tls|mtls> : Specify the transport security mode. none : No TLS security. This is the default. tls : TLS with server authentication only. mtls : Mutual TLS, both server and client authentication.

                 See CERTIFICATES for details about specifying certificates/keys
                 that libnfs must use when using "tls" or "mtls" security.

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. readonly : Set the mount to readonly. 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. rsize=<int> : This is the maximum number of bytes libnfs client will ask in a single READ request. The actual value is the minimum of this and the 'rtmax' value shared by the server in the FSINFO response. The largest rsize value supported is 4,194,304 bytes, i.e., 4MiB. The smallest rsize value supported is 8192 bytes, i.e., 8KiB. The provided value must be a multiple of 4096, else it's rounded down to the nearest 4096 bytes. Default value used when rsize option is not specified, is 1,048,576 bytes, i.e., 1MiB. wsize=<int> : This is the maximum number of bytes libnfs client will send in a single WRITE request. The actual value is the minimum of this and the 'wtmax' value shared by the server in the FSINFO response. The largest wsize value supported is 4,194,304 bytes, i.e., 4MiB. The smallest wsize value supported is 8192 bytes, i.e., 8KiB. The provided value must be a multiple of 4096, else it's rounded down to the nearest 4096 bytes. Default value used when wsize option is not specified, is 1,048,576 bytes, i.e., 1MiB. readdir-buffer=<count> | readdir-buffer=<dircount>,<maxcount> : Set the buffer size for READDIRPLUS, where dircount is the maximum amount of bytes the server should use to retrieve the entry names and maxcount is the maximum size of the response buffer (including attributes). If only one <count> is given it will be used for both. The provided value(s) must be multiple of 4096, else they are rounded down to the nearest 4096 bytes. The actual value is the minimum of this and the 'dtpref' value shared by the server in the FSINFO response. Default is 8192 for both.

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