NetBSD/lib/libpuffs/puffs.3

.\"	$NetBSD: puffs.3,v 1.23 2007/05/15 13:44:47 pooka Exp $
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.\" Copyright (c) 2006, 2007 Antti Kantee.  All rights reserved.
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.Dd May 15, 2007
.Dt PUFFS 3
.Os
.Sh NAME
.Nm puffs
.Nd Pass-to-Userspace Framework File System development interface
.Sh LIBRARY
.Lb libpuffs
.Sh SYNOPSIS
.In puffs.h
.Ft struct puffs_usermount *
.Fo puffs_init
.Fa "struct puffs_ops *pops" "const char *puffsname" "void *private"
.Fa "uint32_t flags"
.Fc
.Ft int
.Fn puffs_domount "struct puffs_usermount *pu" "const char *dir" "int mntflags"
.Ft struct puffs_usermount *
.Fo puffs_mount
.Fa "struct puffs_ops *pops" "const char *dir" "int mntflags"
.Fa "const char *puffsname" "void *private"
.Fa "uint32_t pflags"
.Fc
.Ft int
.Fo puffs_start
.Fa "struct puffs_usermount *pu" "void *rootcookie" "struct statvfs *svfsb"
.Fc
.Ft int
.Fn puffs_getselectable "struct puffs_usermount *pu"
.Ft int
.Fn puffs_setblockingmode "struct puffs_usermount *pu" "int mode"
.Ft int
.Fn puffs_getstate "struct puffs_usermount *pu"
.Ft int
.Fn puffs_setstacksize "struct puffs_usermount *pu" "size_t stacksize"
.Ft void
.Fn puffs_setroot "struct puffs_usermount *pu" "struct puffs_node *node"
.Ft struct puffs_node *
.Fn puffs_getroot "struct puffs_usermount *pu"
.Ft void *
.Fn puffs_getspecific "struct puffs_usermount *pu"
.Ft void
.Fn puffs_setmaxreqlen "struct puffs_usermount *pu" "size_t maxreqlen"
.Ft size_t
.Fn puffs_getmaxreqlen "struct puffs_usermount *pu"
.Ft void
.Fn puffs_setfhsize "struct puffs_usermount *pu" "size_t fhsize" "int flags"
.Ft void
.Fn puffs_setncookiehash "struct puffs_usermount *pu" "int nhashes"
.Ft void
.Fn puffs_ml_loop_fn "struct puffs_usermount *pu"
.Ft void
.Fn puffs_ml_setloopfn "struct puffs_usermount *pu" "puffs_ml_loop_fn lfn"
.Ft void
.Fn puffs_ml_settimeout "struct puffs_usermount *pu" "struct timespec *ts"
.Ft int
.Fn puffs_mainloop "struct puffs_usermount *pu" "int flags"
.Sh DESCRIPTION
.Em IMPORTANT NOTE!
This document describes interfaces which are not yet guaranteed to be
stable.
In case you update your system sources, please recompile everything
and fix complation errors.
If your sources are out-of-sync, incorrect operation may result.
The interfaces in this document will most likely be hugely simplified
in later versions or made transparent to the implementation.
.Pp
.Nm
provides a framework for creating file systems as userspace servers.
Operations are transported from the kernel virtual file system layer
to the concrete implementation behind
.Nm ,
where they are processed and results are sent back to the kernel.
.Pp
It is possible to use
.Nm
in two different ways.
Calling
.Fn puffs_mainloop
takes execution context away from the caller and automatically handles
all requests by using the callbacks.
By using
.Xr puffs_framebuf 3
in conjuction with
.Fn puffs_mainloop ,
it is possible to handle I/O to and from file descriptors.
This is suited e.g. for distributed file servers.
Alternatively, control can be kept with the caller and operations
handled manually using
.Xr puffs_req 3
directly.
.Ss Library operation
Operations on the library always require a pointer to the opaque context
identifier,
.Va struct puffs_usermount .
There are two ways of acquiring this context:
.Fn puffs_init
and
.Fn puffs_mount .
They are equivalent except in the sense that the latter also proceeds
to mount the file system.
The former can be used when special parameters need to be set and
only then proceed with mounting by calling
.Fn puffs_domount .
.Pp
The callbacks are passed as the fields in the structure
.Fa pops .
They can be initialized using the macro
.Fn PUFFSOP_SET pops fsname type opname ,
which will initialize the operation
.Fn puffs_type_opname
in
.Fa pops
to
.Fn fsname_type_opname .
All operations are initialized to a default state with the call
.Fn PUFFSOP_INIT pops .
All of the VFS routines are mandatory, but all of the node operations
with the exception of
.Fn puffs_fs_lookup
are optional.
However, leaving operations blank will naturally have an effect on the
features available from the file system implementation.
The argument
.Fa dir
signifies the mount point,
.Fa mntflags
is the flagset given to
.Xr mount 2 ,
and
.Fa puffsname
is the name of the file system implementation.
The parameter
.Fa private
is stored within the context structure and can be retrieved by
calling
.Fn puffs_getspecific .
Flags for
.Nm
can be given via
.Fa pflags .
Currently the following flags are supported:
.Bl -tag -width "XPUFFS_KFLAG_BUILDPATHX"
.It Dv PUFFS_KFLAG_NOCACHE
Do not cache anything in the kernel.
Currently this means not using the page cache for regular files or
the name cache (directory entry cache) for all files.
This is useful if the file system does not want to include flushing
and invalidation logic in case it is possible to modify the backend
from "under" our view of the file system (a distributed file system,
for example).
.It Dv PUFFS_KFLAG_ALLOPS
This flag requests that all operations are sent to userspace.
Normally the kernel shortcircuits unimplemented operations.
This flag is mostly useful for debugging purposes.
.It Dv PUFFS_KFLAG_WTCACHE
Set the file system cache behaviour as write-through.
This means that all writes are immediately issued to the file server
instead of being flushed in file system sync.
This is useful especially for distributed file systems.
.It Dv PUFFS_KFLAG_IAONDEMAND
Issue inactive only on demand.
If a file server defines the inactive method, call it only if the file
server has explicitly requested that inactive be called for the
node in question.
Once inactive has been called for a node, it will not be called
again unless the request to call inactive is reissued by the file server.
See
.Fn puffs_setback
in
.Xr puffs_ops 3
for more information.
.It Dv PUFFS_FLAG_BUILDPATH
The framework will build a complete path name, which is supplied
with each operation and can be found from the
.Va pn_po.po_full_pcn
field in a
.Vt struct puffs_node .
The option assumes that the framework can map a cookie to a
.Vt struct puffs_node .
See
.Sx Cookies
for more information on cookie mapping.
See
.Xr puffs_path 3
for more information on library calls involving paths.
.It Dv PUFFS_FLAG_HASHPATH
Calculate a hash of the path into the path object field
.Va po_hash .
This hash value is used by
.Fn puffs_path_walkcmp
to avoid doing a full comparison for every path equal in length to
the one searched for.
Especially if the file system uses the abovementioned function, it
is a good idea to define this flag.
.It Dv PUFFS_FLAG_OPDUMP
This option makes the framework dump a textual representation of
each operation before executing it.
It is useful for debugging purposes.
.El
.Pp
The following functions can be used to query or modify the global
state of the file system.
Note, that all calls are not available at all times.
.Bl -tag -width xxxx
.It Fn puffs_getselectable "pu"
Returns a handle to do I/O multiplexing with:
.Xr select 2 ,
.Xr poll 2 ,
and
.Xr kqueue 2
are all examples of acceptable operations.
.It Fn puffs_setblockingmode "pu" "mode"
Sets the library to blocking or non-blocking mode.
Acceptable values for the argument are
.Dv PUFFSDEV_BLOCK
and
.Dv PUFFSDEV_NONBLOCK .
.It Fn puffs_getstate "pu"
Returns the state of the file system.
It is maintained by the framework and is mostly useful for the framework
itself.
Possible values are
.Dv PUFFS_STATE_MOUNTING ,
.Dv PUFFS_STATE_RUNNING ,
.Dv PUFFS_STATE_UNMOUNTING
and
.Dv PUFFS_STATE_UNMOUNTED .
.It Fn puffs_setstacksize "stacksize"
Sets the stack size used when running callbacks.
The default is one megabyte of stack space per request.
See
.Xr puffs_cc 3 .
.It Fn puffs_setroot "pu" "node"
Sets the root node of mount
.Fa pu
to
.Fa "node" .
Setting the root node is currently required only if the path
framework is used, see
.Xr puffs_path 3 .
.Pp
This, if desired, should be done before the file system is activated
with
.Fn puffs_start .
.It Fn puffs_getroot "pu"
Returns the root node set earlier.
.It Fn puffs_getspecific "pu"
Returns the
.Fa private
argument of
.Fn puffs_mount .
.It Fn puffs_setmaxreqlen "pu" "maxreqlen"
In case the file system desires a maximum buffer length different from
the default, the amount
.Fa maxreqlen
will be requested from the kernel when the file system is mounted.
.Pp
It is legal to call this function only between
.Fn puffs_init
and
.Fn puffs_domount .
.It Fn puffs_getmaxreqlen "pu"
Returns the maximum request length the kernel will need for a single
request.
This information can be used to allocate the request buffer and
.B must
be passed as the parameter to
.Fn puffs_req_makeget .
.It Fn puffs_setfhsize "pu" "fhsize" "flags"
Sets the desired file handle size.
This must be called if the file system wishes to support nfs exporting
file systems of the
.Fn fh*
family of function calls.
.Pp
In case all nodes in the file system produce the same length file handle,
it must be supplied as
.Fa fhsize .
In this case, the file system may ignore the length parameters in the
file handle callback routines, as the kernel will always pass the
correct length buffer.
However, if the file handle size varies according to file, the argument
.Fa fhsize
defines the maximum size of a file handle for the file system.
In this case the file system must take care of the handle lengths by
itself in the file handle callbacks, see
.Xr puffs_ops 3
for more information.
Also, the flag
.Dv PUFFS_FHFLAG_DYNAMIC
must be provided in the argument
.Fa flags .
.Pp
In case the file system wants to sanity check its file handle lengths
for the limits of NFS, it can supply
.Dv PUFFS_FHFLAG_NFSV2
and
.Dv PUFFS_FHFLAG_NFSV3
in the
.Fa flags
parameter.
It is especially important to note that these are not directly the
limits specified by the protocols, as the kernel uses some bytes from
the buffer space.
In case the file handles are too large, mount will return an error.
.Pp
It is legal to call this function only between
.Fn puffs_init
and
.Fn puffs_domount .
.It Fn puffs_setncookiehash "pu" "ncookiehash"
The parameter
.Fa ncookiehash
controls the amount of hash buckets the kernel has for reverse lookups
from cookie to vnode.
Technically the default is enough, but a memory/time tradeoff can be
made by increasing this for file systems which know they will have
very many active files.
.Pp
It is legal to call this function only between
.Fn puffs_init
and
.Fn puffs_domount .
.El
.Pp
After the correct setup for the library has been established and the
backend has been initialized (and the file system has been mounted if
.Fn puffs_init
was used to acquire the usermount context!), the file system is made
operational
by calling
.Fn puffs_start .
Immediately after the return of this function the file system must
be ready to process requests.
.Ss Using the built-in eventloop
.Bl -tag -width xxxx
.It Fn puffs_ml_loop_fn pu
Loop function signature.
.It Fn puffs_ml_setloopfn pu lfn
Set loop function to
.Ar lfn .
This function is called once each time the event loop loops.
It is not a well-defined interval, but it can be made fairly regular
by setting the loop timeout by
.Fn puffs_ml_settimeout .
.It Fn puffs_ml_settimeout pu ts
Sets the loop timeout to
.Ar ts
or disables it if
.Ar ts
is
.Dv NULL .
This can be used to roughly control how often the loop callback
.Fn lfn
is called
.It Fn puffs_mainloop pu flags
Handle all requests automatically until the file system is unmounted.
It returns 0 if the file system was succesfully unmounted or \-1 if it
was killed in action.
Unless
.Fa flags
is used to pass
.Dv PUFFSLOOP_NODAEMON ,
.Fn puffs_mainloop
will also detach from the terminal.
.Pp
In case
.Xr puffs_framebuf 3
has been initialized, I/O from the relevant descriptors is processed
automatically by the eventloop.
.El
.Ss Cookies
Every file (regular file, directory, device node, ...) instance is
attached to the kernel using a cookie.
A cookie should uniquely map to a file during its lifetime.
If file instances are kept in memory, a simple strategy is to use
the virtual address of the structure describing the file.
The cookie can be recycled when
.Fn puffs_node_reclaim
is called for a node.
.Pp
For some operations (such as building paths) the framework needs to map
the cookie to the framework-level structure describing a file,
.Vt struct puffs_node .
It is advisable to simply use the
.Vt struct puffs_node
address as a cookie and store file system specific data in the private
portion of
.Vt struct puffs_node .
The library assumes this by default.
If it is not desireable, the file system implementation can call
.Fn puffs_set_cookiemap
to provide an alternative cookie-to-node mapping function.
.Sh SEE ALSO
.Xr puffs_cc 3 ,
.Xr puffs_cred 3 ,
.Xr puffs_flush 3 ,
.Xr puffs_framebuf 3 ,
.Xr puffs_node 3 ,
.Xr puffs_ops 3 ,
.Xr puffs_path 3 ,
.Xr puffs_req 3 ,
.Xr puffs_suspend 3 ,
.Xr puffs 4
.Rs
.%A Antti Kantee
.%D March 2007
.%J Proceedings of AsiaBSDCon 2007
.%P pp. 29-42
.%T puffs - Pass-to-Userspace Framework File System
.Re
.Sh HISTORY
An unsupported experimental version of
.Nm
first appeared in
.Nx 4.0 .
.Sh AUTHORS
.An Antti Kantee Aq pooka@iki.fi
.Sh BUGS
Under construction.