PUFFS_FRAMEBUF(3)       NetBSD Library Functions Manual      PUFFS_FRAMEBUF(3)

NAME
     puffs_framebuf -- buffering and event handling for networked file systems

LIBRARY
     puffs Convenience Library (libpuffs, -lpuffs)

SYNOPSIS
     #include <puffs.h>

     struct puffs_framebuf *
     puffs_framebuf_make();

     void
     puffs_framebuf_destroy(struct puffs_framebuf *pufbuf);

     void
     puffs_framebuf_recycle(struct puffs_framebuf *pufbuf);

     int
     puffs_framebuf_reserve_space(struct puffs_framebuf *pufbuf,
         size_t space);

     int
     puffs_framebuf_putdata(struct puffs_framebuf *pufbuf, const void *data,
         size_t dlen);

     int
     puffs_framebuf_putdata_atoff(struct puffs_framebuf *pufbuf,
         size_t offset, const void *data, size_t dlen);

     int
     puffs_framebuf_getdata(struct puffs_framebuf *pufbuf, void *data,
         size_t dlen);

     int
     puffs_framebuf_getdata_atoff(struct puffs_framebuf *pufbuf,
         size_t offset, void *data, size_t dlen);

     size_t
     puffs_framebuf_telloff(struct puffs_framebuf *pufbuf);

     size_t
     puffs_framebuf_tellsize(struct puffs_framebuf *pufbuf);

     size_t
     puffs_framebuf_remaining(struct puffs_framebuf *pufbuf);

     int
     puffs_framebuf_seekset(struct puffs_framebuf *pufbuf, size_t offset);

     int
     puffs_framebuf_getwindow(struct puffs_framebuf *pufbuf, size_t offset,
         void **winp, size_t *winlen);

     int
     puffs_framev_enqueue_cc(struct puffs_cc *pcc, int fd,
         struct puffs_framebuf *pufbuf, int flags);

     void
     puffs_framev_cb(struct puffs_usermount *pu, int fd,
         struct puffs_framebuf *pufbuf, void *arg, int flags, int error);

     void
     puffs_framev_enqueue_cb(struct puffs_usermount *pu, int fd,
         struct puffs_framebuf *pufbuf, puffs_framebuf_cb fcb, void *fcb_arg,
         int flags);

     void
     puffs_framev_enqueue_justsend(struct puffs_usermount *pu, int fd,
         struct puffs_framebuf *pufbuf, int waitreply, int flags);

     void
     puffs_framev_enqueue_directsend(struct puffs_usermount *pu, int fd,
         struct puffs_framebuf *pufbuf, int flags);

     void
     puffs_framev_enqueue_directreceive(struct puffs_usermount *pu, int fd,
         struct puffs_framebuf *pufbuf, int flags);

     int
     puffs_framev_framebuf_ccpromote(struct puffs_framebuf *pufbuf,
         struct puffs_cc *pcc);

     int
     puffs_framev_enqueue_waitevent(struct puffs_cc *pcc, int fd, int *what);

     int
     puffs_framev_readframe_fn(struct puffs_usermount *pu,
         struct puffs_framebuf *pufbuf, int fd, int *done);

     int
     puffs_framev_writeframe_fn(struct puffs_usermount *pu,
         struct puffs_framebuf *pufbuf, int fd, int *done);

     int
     puffs_framev_cmpframe_fn(struct puffs_usermount *pu,
         struct puffs_framebuf *cmp1, struct puffs_framebuf *cmp2,
         int *notresp);

     void
     puffs_framev_gotframe_fn(struct puffs_usermount *pu,
         struct puffs_framebuf *pufbuf);

     void
     puffs_framev_fdnotify_fn(struct puffs_usermount *pu, int fd, int what);

     void
     puffs_framev_init(struct puffs_usermount *pu,
         puffs_framev_readframe_fn rfb, puffs_framev_writeframe_fn wfb,
         puffs_framev_cmpframe_fn cmpfb, puffs_framev_gotframe_fn gotfb,
         puffs_framev_fdnotify_fn fdnotfn);

     int
     puffs_framev_addfd(struct puffs_usermount *pu, int fd, int what);

     int
     puffs_framev_enablefd(struct puffs_usermount *pu, int fd, int what);

     int
     puffs_framev_disablefd(struct puffs_usermount *pu, int fd, int what);

     int
     puffs_framev_removefd(struct puffs_usermount *pu, int fd, int error);

     void
     puffs_framev_unmountonclose(struct puffs_usermount *pu, int fd,
         int what);

DESCRIPTION
     The puffs_framebuf routines provide buffering and an event loop struc-
     tured around the buffers.  It operates on top of the puffs continuation
     framework, puffs_cc(3), and multiplexes execution automatically to an
     instance whenever one is runnable.

     The file system is entered in three different ways:

              An event arrives from the kernel and the puffs_ops(3) callbacks
               are called to start processing the event.

              A file system which has sent out a request receives a response.
               Execution is resumed from the place where the file system
               yielded.

              A request from a peer arrives.  A request is an incoming PDU
               which is not a response to any outstanding request.

     puffs_framebuf is used by defining various callbacks and providing I/O
     descriptors, which are then monitored for activity by the library.  A
     descriptor, when present, can be either enabled or disabled for input and
     output.  If a descriptor is not enabled for a certain direction, the
     callbacks will not be called even if there were activity on the descrip-
     tor.  For example, even if a network socket has been added and there is
     input data in the socket buffer, the read callback will be called only if
     the socket has been enabled for reading.

     File descriptors are treated like sockets: they have two sides, a read
     side and a write side.  The framework determines that one side of the
     descriptor has been closed if the supplied I/O callbacks return an error
     or if the I/O multiplexing call says a side has been closed.  It is still
     possible, from the framework perspective, to write to a file descriptor
     whose read side is closed.  However, it is not possible to wait for a
     response on such a file descriptor.  Conversely, it is possible to read
     responses from a descriptor whose write side is closed.  It should be
     stressed that the implementation underlying the file descriptor might not
     support this.

     The following callbacks can be defined, cf.  puffs_framev_init(), and all
     are optional.  None of them should block, because this would cause the
     entire file server to block.  One option is to make the descriptors non-
     blocking before adding them.

     rfb        Read a frame from the file descriptor onto the specified
                buffer.

     wfb        Write a frame from the specified buffer into the file descrip-
                tor.

     cmpfb      Identify if a buffer is the response to the specified buffer.

     gotfb      Called iff no outstanding request matches the incoming frame.
                In other words, this is called when we receive a request from
                a peer.

     fdnotfn    Receive notifications about a change-of-state in a file
                descriptor's status.

     Better descriptions for each callback are given below.

     The buffers of puffs_framebuf provide automatic memory management of
     buffers for the file servers.  They provide a cursor to the current
     buffer offset.  Reading or writing data through the normal routines will
     advance that cursor.  Additionally, the buffer size is provided to the
     user.  It represents the maximum offset where data was written.

     Generally the write functions will fail if the cannot allocate enough
     memory to satisfy the buffer length requirements.  Read functions will
     fail if the amount of data written to the buffer is not large enough to
     satisfy the read.

     puffs_framebuf_make()
           Create a buffer.  Return the address of the buffer or NULL in case
           no memory was available.

     puffs_framebuf_destroy(pufbuf)
           Free memory used by buffer.

     puffs_framebuf_recycle(pufbuf)
           Reset offsets so that buffer can be reused.  Does not free memory
           or reallocate memory.

     puffs_framebuf_reserve_space(pufbuf, space)
           Make sure that the buffer has space bytes of available memory
           starting from the current offset.  This is not strictly necessary,
           but can be used for optimizations where it is known in advance how
           much memory will be required.

     puffs_framebuf_putdata(pufbuf, data, dlen)
           Write dlen amount of data from the address data into the buffer.
           Moves the offset cursor forward dlen bytes.

     puffs_framebuf_putdata_atoff(pufbuf, offset, data, dlen)
           Like puffs_framebuf_putdata(), except writes data at buffer offset
           offset.  It is legal to write past the current end of the buffer.
           Does NOT modify the current offset cursor.

     puffs_framebuf_getdata(pufbuf, data, dlen)
           Read dlen bytes of data from the buffer into data.  Advances the
           offset cursor.

     puffs_framebuf_getdata_atoff(pufbuf, offset, data, dlen)
           Read data from buffer position offset.  Does NOT modify the offset
           cursor.

     puffs_framebuf_telloff(pufbuf)
           Return the offset into the buffer.

     puffs_framebuf_tellsize(pufbuf)
           Return the maximum offset where data has been written, i.e. buffer
           size.

     puffs_framebuf_remaining(pufbuf)
           Distance from current offset to the end of the buffer, i.e. size-
           offset.

     puffs_framebuf_seekset(pufbuf, offset)
           Set the offset cursor to the position offset.  This does NOT modify
           the buffer size, but reserves at least enough memory memory for a
           write to offset and will fail if memory cannot be allocated.

     puffs_framebuf_getwindow(pufbuf, offset, winp, winlen)
           Get a direct memory window into the buffer starting from offset.
           The maximum mapped window size will be winlen bytes, but this rou-
           tine might return a smaller window and the caller should always
           check the actual mapped size after the call.  The window is
           returned in winp.  This function not modify the buffer offset, but
           it DOES set the buffer size to offset + winlen in case that value
           is greater than the current size.  The window is valid until the
           next until the next puffs_framebuf() call operating on the buffer
           in question.

     puffs_framev_enqueue_cc(pcc, fd, pufbuf, flags)
           Add the buffer pufbuf to outgoing queue of descriptor fd and yield
           with the continuation pcc.  Execution is resumed once a response is
           received.  Returns 0 if the buffer was successfully enqueued (not
           necessarily delivered) and non-zero to signal a non-recoverable
           error.

           Usually the buffer is placed at the end of the output queue.  How-
           ever, if flags contains PUFFS_FBQUEUE_URGENT, pufbuf is placed in
           the front of the queue to be sent immediately after the current PDU
           (if any) has been sent.

     puffs_framev_enqueue_cb(pu, fd, pufbuf, fcb, fcb_arg, flags)
           Enqueue the buffer pufbuf for outgoing data and immediately return.
           Once a response arrives, the callback fcb() will be called with the
           argument fcb_arg.  The callback function fcb() is responsible for
           freeing the buffer.  Returns 0 if the buffer was successfully
           enqueued (not necessarily delivered) and non-zero to signal a non-
           recoverable error.

           See puffs_framev_enqueue_cc() for flags.

     puffs_framev_cb(pu, pufbuf, arg, error)
           Callback function.  Called when a response to a specific request
           arrives from the server.  If error is non-zero, the framework was
           unable to obtain a response and the function should not examine the
           contents of pufbuf, only do resource cleanup.  May not block.

     puffs_framev_enqueue_justsend(pu, fd, pufbuf, waitreply, flags)
           Enqueue the buffer pufbuf for outgoing traffic and immediately
           return.  The parameter waitreply can be used to control if the
           buffer is to be freed immediately after sending of if a response is
           expected and the buffer should be freed only after the response
           arrives (receiving an unexpected message from the server is treated
           as an error).  Returns 0 if the buffer was successfully enqueued
           (not necessarily delivered) and non-zero to signal a non-recover-
           able error.

           See puffs_framev_enqueue_cc() for flags.

     puffs_framev_enqueue_directsend(pcc, fd, pufbuf, flags)
           Acts like puffs_framev_enqueue_justsend() with the exception that
           the call yields until the frame has been sent.  As opposed to
           puffs_framev_enqueue_cc(), the routine does not wait for input, but
           returns immediately after sending the frame.

           See puffs_framev_enqueue_cc() for flags.

     puffs_framev_enqueue_directreceive(pcc, fd, pufbuf, flags)
           Receive data into pufbuf.  This routine yields until a complete
           frame has been read into the buffer by the readframe routine.

           See puffs_framev_enqueue_cc() for flags.

     puffs_framev_framebuf_ccpromote(pufbuf, pcc)
           Promote the framebuffer pufbuf sent with puffs_framev_enqueue_cb()
           or puffs_framev_enqueue_justsend() to a wait using pcc and yield
           until the result arrives.  The response from the file server for
           pufbuf must not yet have arrived.  If sent with
           puffs_framev_enqueue_justsend(), the call must be expecting a
           response.

     puffs_framev_enqueue_waitevent(pcc, fd, what)
           Waits for an event in what to happen on file descriptor fd.  The
           events which happened are returned back in what.  The possible
           events are PUFFS_FBIO_READ, PUFFS_FBIO_WRITE, and PUFFS_FBIO_ERROR,
           specifying read, write and error conditions, respectively.  Error
           is always checked.

           This call does not depend on if the events were previously enabled
           on the file descriptor - the specified events are always checked
           regardless.

           There is currently no other way to cancel or timeout a call except
           by removing the file descriptor in question.  This may change in
           the future.

     puffs_framev_readframe_fn(pu, pufbuf, fd, done)
           Callback function.  Read at most one frame from file descriptor fd
           into the buffer pufbuf.  If a complete frame is read, the value
           pointed to by done must be set to 1.  This function should return 0
           on success (even if a complete frame was not yet read) and a non-
           zero errno to signal a fatal error.  In case a fatal error is
           returned, the read side of the file descriptor is marked closed.
           This routine will be called with the same buffer argument until a
           complete frame has been read.  May not block.

     puffs_framev_writeframe_fn(pu, pufbuf, fd, done)
           Write the frame contained in pufbuf to the file descriptor fd.  In
           case the entire frame is successfully written, *done should be set
           to 1.  This function should return 0 on success (even if a complete
           frame was not yet written) and a non-zero errno to signal a fatal
           error.  In case a fatal error is returned, the write side of the
           file descriptor is marked closed.  This routine will be called with
           the same buffer argument until the complete frame has been written.
           May not block.

           It is a good idea to make sure that this function can handle a pos-
           sible SIGPIPE caused by a closed connection.  For example, the file
           server can opt to trap SIGPIPE or, if writing to a socket, call
           send() with the flag MSG_NOSIGNAL instead of using write().

     puffs_framev_cmpframe_fn(pu, pufbuf_cmp1, pufbuf_cmp2, notresp)
           Compare the file system internal request tags in pufbuf_cmp1 and
           pufbuf_cmp2.  Should return 0 if the tags are equal, 1 if first
           buffer's tag is greater than the second and -1 if it is smaller.
           The definitions "greater" and "smaller" are used transparently by
           the library, e.g. like qsort(3).  If it can be determined from
           pufbuf_cmp1 that it is not a response to any outstanding request,
           notresp should be set to non-zero.  This will cause puffs_framebuf
           to skip the test of the buffer against the rest of the outstanding
           request.  May not block.

     puffs_framev_gotframe_fn(pu, pufbuf)
           Called when no outstanding request matches an incoming frame.  The
           ownership of pufbuf is transferred to the called function and must
           be destroyed once processing is over.  May not block.

     puffs_framev_fdnotify_fn(pu, fd, what)
           Is called when the read or write side of the file descriptor fd is
           closed.  It is called once for each side, the bitmask parameter
           what specified what is currently closed: PUFFS_FBIO_READ and
           PUFFS_FBIO_WRITE for read and write, respectively.

     puffs_framev_init(pu, rfb, wfb, cmpfb, gotfb, fdnotfn)
           Initializes the given callbacks to the system.  They will be used
           when puffs_mainloop() is called.  The framework provides the rou-
           tines puffs_framev_removeonclose() and
           puffs_framev_unmountonclose(), which can be given as fdnotfn.  The
           first one removes the file descriptor once both sides are closed
           while the second one unmounts the file system and exits the main-
           loop.

     puffs_framev_addfd(pu, fd, what)
           Add file descriptor fd to be handled by the framework.  It is legal
           to add a file descriptor either before calling puffs_mainloop() or
           at time when running.  The parameter what controls enabling of
           input and output events and can be a bitwise combination of
           PUFFS_FBIO_READ and PUFFS_FBIO_WRITE.  If not specified, the
           descriptor will be in a disabled state.

     puffs_framev_enablefd(pu, fd, what)
           Enable events of type what for file descriptor fd.

     puffs_framev_disablefd(pu, fd, what)
           Disable events of type what for file descriptor fd.

     puffs_framev_removefd(pu, fd, error)
           Remove file descriptor fd from the list of descriptors handled by
           the framework.  Removing a file descriptor causes all operations
           blocked either on output or input to be released with the error
           value error.  In case 0 is supplied as this parameter, ECONNRESET
           is used.

           The file system must explicitly remove each fd it has added.  A
           good place to do this is puffs_framev_fdnotify_fn() or
           puffs_node_reclaim(), depending a little on the structure of the
           file system.

     puffs_framev_unmountonclose(pu, fd, what)
           This is library provided convenience routine for
           puffs_framev_fdnotify_fn().  It unmounts the file system when both
           the read and write side are closed.  It is useful for file systems
           such as mount_psshfs(8) which depend on a single connection.

CODE REFERENCES
     The current users of puffs_framebuf in the tree are mount_psshfs(8) and
     mount_9p(8).  See src/usr.sbin/puffs/mount_psshfs and
     src/usr.sbin/puffs/mount_9p for the respective usage examples.

RETURN VALUES
     These functions generally return -1 to signal error and set errno to
     indicate the type of error.

SEE ALSO
     puffs(3), puffs_cc(3), puffs_ops(3)

     Antti Kantee, Using puffs for Implementing Client-Server Distributed File
     Systems, Helsinki University of Technology, Tech Report TKK-TKO-B157,
     September 2007.

     Antti Kantee, "Send and Receive of File System Protocols: Userspace
     Approach With puffs", Proceedings of AsiaBSDCon 2008, pp. 55-70, March
     2008.

NetBSD 6.0                     September 6, 2008                    NetBSD 6.0

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