NAME
puffs
—
Pass-to-Userspace Framework File System
development interface
LIBRARY
library “libpuffs”
SYNOPSIS
#include
<puffs.h>
struct puffs_usermount *
puffs_init
(struct puffs_ops
*pops, const char *mntfromname,
const char *puffsname, void
*private, uint32_t flags);
int
puffs_mount
(struct puffs_usermount
*pu, const char *dir, int
mntflags, puffs_cookie_t root_cookie);
int
puffs_getselectable
(struct
puffs_usermount *pu);
int
puffs_setblockingmode
(struct
puffs_usermount *pu, int
mode);
int
puffs_getstate
(struct
puffs_usermount *pu);
int
puffs_setstacksize
(struct
puffs_usermount *pu,
size_t stacksize);
void
puffs_setroot
(struct
puffs_usermount *pu,
struct puffs_node
*node);
void
puffs_setrootinfo
(struct
puffs_usermount *pu, enum vtype vt,
vsize_t vsize, dev_t rdev);
struct puffs_node *
puffs_getroot
(struct
puffs_usermount *pu);
void *
puffs_getspecific
(struct
puffs_usermount *pu);
void
puffs_setspecific
(struct
puffs_usermount *pu, void
*private);
void
puffs_setmaxreqlen
(struct
puffs_usermount *pu,
size_t maxreqlen);
size_t
puffs_getmaxreqlen
(struct
puffs_usermount *pu);
void
puffs_setfhsize
(struct
puffs_usermount *pu,
size_t fhsize,
int flags);
void
puffs_setncookiehash
(struct
puffs_usermount *pu, int
nhashes);
void
puffs_ml_loop_fn
(struct
puffs_usermount *pu);
void
puffs_ml_setloopfn
(struct
puffs_usermount *pu,
puffs_ml_loop_fn
lfn);
void
puffs_ml_settimeout
(struct
puffs_usermount *pu,
struct timespec *ts);
int
puffs_daemon
(struct
puffs_usermount *pu, int
nochdir, int
noclose);
int
puffs_mainloop
(struct
puffs_usermount *pu);
int
puffs_unmountonsignal
(int
sig, bool
ignoresig);
int
puffs_dispatch_create
(struct
puffs_usermount *pu, struct puffs_framebuf *pb,
struct puffs_cc **pccp);
int
puffs_dispatch_exec
(struct
puffs_cc *pcc, struct
puffs_framebuf **pbp);
DESCRIPTION
puffs
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
puffs
, where they are processed and results are sent
back to the kernel.
It is possible to use
puffs
in two different ways. Calling
puffs_mainloop
()
takes execution context away from the caller and automatically handles all
requests by using the callbacks. By using
puffs_framebuf(3) in conjuction with
puffs_mainloop
(), it is possible to handle I/O to
and from file descriptors. This is suited e.g. for distributed file
servers.
Library operation
Operations on the library always require a pointer to the opaque
context identifier, struct puffs_usermount. It is
obtained by calling puffs_init
().
puffs
operates using
operation callbacks. They can be initialized using the macro
PUFFSOP_SET
(pops,
fsname, type,
opname), which will initialize the operation
puffs_type_opname
()
in pops to
fsname_type_opname
().
All operations are initialized to a default state with the call
PUFFSOP_INIT
(pops).
All of the VFS routines are mandatory, but all of the node operations with
the exception of
puffs_node_lookup
()
are optional. However, leaving operations blank will naturally have an
effect on the features available from the file system implementation.
puffs_init
(pops, mntfromname, puffsname, private, flags)- Initializes the library context. pops specifies the
callback operations vector. mntfromname is device
the file system is mounted from. This can be for example a block device
such as /dev/wd0a or, if the file system is pseudo
file system, the
puffs
device name can be given by_PATH_PUFFS
. This value is used for example in the first column of the output of mount(8) and df(1). puffsname is the file system type. It will always be prepended with the string "puffs|". If possible, file server binaries should be named using the format "mount_myfsnamehere" and this value should equal "myfsnamehere". A file system specific context pointer can optionally be given in private. This can be retrieved bypuffs_getspecific
(). Flags forpuffs
can be given via flags. Currently the following flags are supported:PUFFS_KFLAG_NOCACHE_NAME
- Do not enter pathname components into the name cache. This means that every time the kernel does a lookup for a componentname, the file server will be consulted.
PUFFS_KFLAG_NOCACHE_PAGE
- Do not use the page cache. This means that all reads and writes to regular file are propagated to the file server for handling. This option makes a difference only for regular files.
PUFFS_KFLAG_NOCACHE
- An alias for both
PUFFS_KFLAG_NOCACHE_NAME
andPUFFS_KFLAG_NOCACHE_PAGE
. 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.
PUFFS_KFLAG_WTCACHE
- Set the file system cache behavior 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.
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
puffs_setback
() in puffs_ops(3) for more information. PUFFS_KFLAG_LOOKUP_FULLPNBUF
- This flag affects only the parameter pcn to
puffs_node_lookup
(). If this flag is not given, only the next pathname component under lookup is found from pcn->pcn_name. If this flag is given, the full path the kernel was asked to resolve can be found from there. PUFFS_FLAG_BUILDPATH
- The framework will build a complete path name, which is supplied with each operation and can be found from the pcn_po_full.po_path field in a struct puffs_cn. The option assumes that the framework can map a cookie to a struct puffs_node. See Cookies for more information on cookie mapping. See puffs_path(3) for more information on library calls involving paths.
PUFFS_FLAG_HASHPATH
- Calculate a hash of the path into the path object field
po_hash. This hash value is used by
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. PUFFS_FLAG_PNCOOKIE
- Tell puffs that cookies map to struct pnode.
This is automagically set if
puffs_pn_new
() is called. PUFFS_KFLAG_CACHE_FS_TTL
- Enforce name and attribute caches based on file system-supplied TTL.
In lookup, create, mknod, mkdir, and symlink, the file system must
update the node attributes, their TTL, and the node name TTL through
puffs_newinfo_setva
(),puffs_newinfo_setvattl
(), andpuffs_newinfo_setcnttl
().Additionally,
puffs_node_getattr_ttl
() andpuffs_node_setattr_ttl
() will be called instead ofpuffs_node_getattr
() andpuffs_node_setattr
(). PUFFS_KFLAG_CACHE_DOTDOT
- Never send lookups for “..” to the file system. Parent vnodes are all kept active until their children are reclaimed.
PUFFS_KFLAG_NOFLUSH_META
- Do not send metadata cache flushes for time and size to the file system, which should take care of updating the values on its own.
PUFFS_FLAG_OPDUMP
- This option makes the framework dump a textual representation of each operation before executing it. It is useful for debugging purposes.
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.
puffs_getselectable
(pu)- Returns a handle to do I/O multiplexing with: select(2), poll(2), and kqueue(2) are all examples of acceptable operations.
puffs_setblockingmode
(pu, mode)- Sets the file system upstream access to blocking or non-blocking mode.
Acceptable values for the argument are
PUFFSDEV_BLOCK
andPUFFSDEV_NONBLOCK
.This routine can be called only after calling
puffs_mount
(). 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
PUFFS_STATE_BEFOREMOUNT
,PUFFS_STATE_RUNNING
,PUFFS_STATE_UNMOUNTING
andPUFFS_STATE_UNMOUNTED
. puffs_setstacksize
(pu, stacksize)- Sets the stack size used when running callbacks. The default is
PUFFS_STACKSIZE_DEFAULT
bytes of stack space per request. The minimum stacksize is architecture-dependent and can be specified by using the opaque constantPUFFS_STACKSIZE_MIN
. puffs_setroot
(pu, node)- Sets the root node of mount pu to node. Setting the root node is currently required only if the path framework is used, see puffs_path(3).
puffs_setrootinfo
(pu, vt, vsize, rdev)- The default root node is a directory. In case the file system wants
something different, it can call this function and set the type, size and
possible device type to whatever it wants. This routine is independent of
puffs_setroot
(). puffs_getroot
(pu)- Returns the root node set earlier.
puffs_getspecific
(pu)- Returns the private argument of
puffs_init
(). puffs_setspecific
(pu, private)- Can be used to set the specific data after the call to
puffs_init
(). puffs_setmaxreqlen
(pu, maxreqlen)- In case the file system desires a maximum buffer length different from the
default, the amount maxreqlen will be requested from
the kernel when the file system is mounted.
It is legal to call this function only between
puffs_init
() andpuffs_mount
().NOTE This does not currently work.
puffs_getmaxreqlen
(pu)- Returns the maximum request length the kernel will need for a single
request.
NOTE This does not currently work.
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
fh*
() family of function calls.In case all nodes in the file system produce the same length file handle, it must be supplied as 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 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 puffs_ops(3) for more information. Also, the flag
PUFFS_FHFLAG_DYNAMIC
must be provided in the argument flags.In case the file system wants to sanity check its file handle lengths for the limits of NFS, it can supply
PUFFS_FHFLAG_NFSV2
andPUFFS_FHFLAG_NFSV3
in the 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.It is legal to call this function only between
puffs_init
() andpuffs_mount
(). - The parameter 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.
It is legal to call this function only between
puffs_init
() andpuffs_mount
().
After the correct setup for the library has
been established and the backend has been initialized the file system is
made operational by calling
puffs_mount
().
After this function returns the file system should start processing
requests.
puffs_mount
(pu, dir, mntflags, root_cookie)- pu is the library context pointer from
puffs_init
(). The argument dir signifies the mount point and mntflags is the flagset given to mount(2). The value root_cookie will be used as the cookie for the file system root node.
Using the built-in eventloop
puffs_ml_loop_fn
(pu)- Loop function signature.
puffs_ml_setloopfn
(pu, lfn)- Set loop function to 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
puffs_ml_settimeout
(). puffs_ml_settimeout
(pu, ts)- Sets the loop timeout to ts or disables it if
ts is
NULL
. This can be used to roughly control how often the loop callbacklfn
() is called puffs_daemon
(pu, nochdir, noclose)- Detach from the console like
daemon
(3). This call synchronizes withpuffs_mount
() and the foreground process does not exit before the file system mount call has returned from the kernel. Since this routine internally calls fork, it has to be called beforepuffs_mount
(). puffs_mainloop
(pu, flags)- Handle all requests automatically until the file system is unmounted. It
returns 0 if the file system was successfully unmounted or -1 if it was
killed in action.
In case puffs_framebuf(3) has been initialized, I/O from the relevant descriptors is processed automatically by the eventloop.
puffs_unmountonsignal
(signum, ignoresig)- Cause all file servers within the process to initiate unmount upon receipt
of signal signum. This works only for servers which
call
puffs_mainloop
() and must be called before any server within the process enters the mainloop. The process signal handler is still called before starting the unmount procedure. The parameter ignoresig is provided as a convenience and tells if to install a signal handler to ignore sig so that the process will not e.g. terminate based on the default action before the file system unmount can be initiated. puffs_dispatch_create
(pu, pb, pccp)puffs_dispatch_exec
(pcc, pbp)- In case the use of
puffs_mainloop
() is not possible, requests may be dispatched manually. However, as this is less efficient than using the mainloop, it should never be the first preference.Calling
puffs_dispatch_create
() creates a dispatch request. The argument pb should contains a valid request and upon success pccp will contain a valid request context. This context is passed topuffs_dispatch_exec
() to execute the request. If the request yielded before completing, the routine returns 0, otherwise 1. When the routine completes, pcc is made invalid and a pointer to the processed buffer is placed in pbp. It is the responsibility of the caller to send the response (if necessary) and destroy the buffer.See puffs_cc(3) and puffs_framebuf(3) for further information.
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
puffs_node_reclaim
()
is called for a node.
For some operations (such as building
paths) the framework needs to map the cookie to the framework-level
structure describing a file, struct puffs_node. It is
advisable to simply use the struct puffs_node address
as a cookie and store file system specific data in the private portion of
struct puffs_node. The library assumes this by
default. If it is not desirable, the file system implementation can call
puffs_set_cookiemap
()
to provide an alternative cookie-to-node mapping function.
SEE ALSO
mount(2), puffs_cc(3), puffs_cred(3), puffs_flush(3), puffs_framebuf(3), puffs_node(3), puffs_ops(3), puffs_path(3), refuse(3), puffs(4)
Antti Kantee, puffs - Pass-to-Userspace Framework File System, Proceedings of AsiaBSDCon 2007, pp. 29-42, March 2007.
Antti Kantee, Using puffs for Implementing Client-Server Distributed File Systems, Helsinki University of Technology, Tech Report TKK-TKO-B157, September 2007.
Antti Kantee and Alistair Crooks, ReFUSE: Userspace FUSE Reimplementation Using puffs, EuroBSDCon 2007, September 2007.
Antti Kantee, Send and Receive of File System Protocols: Userspace Approach With puffs, Proceedings of AsiaBSDCon 2008, pp. 55-70, March 2008.
HISTORY
An unsupported experimental version of
puffs
first appeared in NetBSD
4.0. A stable version appeared in NetBSD
5.0.
AUTHORS
Antti Kantee <pooka@iki.fi>