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[minix3.git] / lib / libpuffs / puffs_framebuf.3

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.Dd September 6, 2008
.Dt PUFFS_FRAMEBUF 3
.Os
.Sh NAME
.Nm puffs_framebuf
.Nd buffering and event handling for networked file systems
.Sh LIBRARY
.Lb libpuffs
.Sh SYNOPSIS
.In puffs.h
.Ft struct puffs_framebuf *
.Fn puffs_framebuf_make
.Ft void
.Fn puffs_framebuf_destroy "struct puffs_framebuf *pufbuf"
.Ft void
.Fn puffs_framebuf_recycle "struct puffs_framebuf *pufbuf"
.Ft int
.Fn puffs_framebuf_reserve_space "struct puffs_framebuf *pufbuf" "size_t space"
.Ft int
.Fo puffs_framebuf_putdata
.Fa "struct puffs_framebuf *pufbuf" "const void *data" "size_t dlen"
.Fc
.Ft int
.Fo puffs_framebuf_putdata_atoff
.Fa "struct puffs_framebuf *pufbuf" "size_t offset" "const void *data"
.Fa "size_t dlen"
.Fc
.Ft int
.Fo puffs_framebuf_getdata
.Fa "struct puffs_framebuf *pufbuf" "void *data" "size_t dlen"
.Fc
.Ft int
.Fo puffs_framebuf_getdata_atoff
.Fa "struct puffs_framebuf *pufbuf" "size_t offset"
.Fa "void *data" "size_t dlen"
.Fc
.Ft size_t
.Fn puffs_framebuf_telloff "struct puffs_framebuf *pufbuf"
.Ft size_t
.Fn puffs_framebuf_tellsize "struct puffs_framebuf *pufbuf"
.Ft size_t
.Fn puffs_framebuf_remaining "struct puffs_framebuf *pufbuf"
.Ft int
.Fn puffs_framebuf_seekset "struct puffs_framebuf *pufbuf" "size_t offset"
.Ft int
.Fo puffs_framebuf_getwindow
.Fa "struct puffs_framebuf *pufbuf" "size_t offset"
.Fa "void **winp" "size_t *winlen"
.Fc
.Ft int
.Fo puffs_framev_enqueue_cc
.Fa "struct puffs_cc *pcc" "int fd" "struct puffs_framebuf *pufbuf" "int flags"
.Fc
.Ft void
.Fo puffs_framev_cb
.Fa "struct puffs_usermount *pu" "int fd" "struct puffs_framebuf *pufbuf"
.Fa "void *arg" "int flags"
.Fa "int error"
.Fc
.Ft void
.Fo puffs_framev_enqueue_cb
.Fa "struct puffs_usermount *pu" "int fd" "struct puffs_framebuf *pufbuf"
.Fa "puffs_framebuf_cb fcb" "void *fcb_arg" "int flags"
.Fc
.Ft void
.Fo puffs_framev_enqueue_justsend
.Fa "struct puffs_usermount *pu" "int fd" "struct puffs_framebuf *pufbuf"
.Fa "int waitreply" "int flags"
.Fc
.Ft void
.Fo puffs_framev_enqueue_directsend
.Fa "struct puffs_usermount *pu" "int fd" "struct puffs_framebuf *pufbuf"
.Fa "int flags"
.Fc
.Ft void
.Fo puffs_framev_enqueue_directreceive
.Fa "struct puffs_usermount *pu" "int fd" "struct puffs_framebuf *pufbuf"
.Fa "int flags"
.Fc
.Ft int
.Fo puffs_framev_framebuf_ccpromote
.Fa "struct puffs_framebuf *pufbuf" "struct puffs_cc *pcc"
.Fc
.Ft int
.Fn puffs_framev_enqueue_waitevent "struct puffs_cc *pcc" "int fd" "int *what"
.Ft int
.Fo puffs_framev_readframe_fn
.Fa "struct puffs_usermount *pu" "struct puffs_framebuf *pufbuf"
.Fa "int fd" "int *done"
.Fc
.Ft int
.Fo puffs_framev_writeframe_fn
.Fa "struct puffs_usermount *pu" "struct puffs_framebuf *pufbuf"
.Fa "int fd" "int *done"
.Fc
.Ft int
.Fo puffs_framev_cmpframe_fn
.Fa "struct puffs_usermount *pu"
.Fa "struct puffs_framebuf *cmp1" "struct puffs_framebuf *cmp2" "int *notresp"
.Fc
.Ft void
.Fo puffs_framev_gotframe_fn
.Fa "struct puffs_usermount *pu" "struct puffs_framebuf *pufbuf"
.Fc
.Ft void
.Fo puffs_framev_fdnotify_fn
.Fa "struct puffs_usermount *pu" "int fd" "int what"
.Fc
.Ft void
.Fo puffs_framev_init
.Fa "struct puffs_usermount *pu"
.Fa "puffs_framev_readframe_fn rfb" "puffs_framev_writeframe_fn wfb"
.Fa "puffs_framev_cmpframe_fn cmpfb" "puffs_framev_gotframe_fn gotfb"
.Fa "puffs_framev_fdnotify_fn fdnotfn"
.Fc
.Ft int
.Fn puffs_framev_addfd "struct puffs_usermount *pu" "int fd" "int what"
.Ft int
.Fn puffs_framev_enablefd "struct puffs_usermount *pu" "int fd" "int what"
.Ft int
.Fn puffs_framev_disablefd "struct puffs_usermount *pu" "int fd" "int what"
.Ft int
.Fn puffs_framev_removefd "struct puffs_usermount *pu" "int fd" "int error"
.Ft void
.Fo puffs_framev_unmountonclose
.Fa "struct puffs_usermount *pu" "int fd" "int what"
.Fc
.Sh DESCRIPTION
The
.Nm
routines provide buffering and an event loop structured around the
buffers.
It operates on top of the puffs continuation framework,
.Xr puffs_cc 3 ,
and multiplexes execution automatically to an instance whenever
one is runnable.
.Pp
The file system is entered in three different ways:
.Bl -bullet -offset indent
.It
An event arrives from the kernel and the
.Xr puffs_ops 3
callbacks are called to start processing the event.
.It
A file system which has sent out a request receives a response.
Execution is resumed from the place where the file system yielded.
.It
A request from a peer arrives.
A request is an incoming PDU which is not a response to any outstanding
request.
.El
.Pp
.Nm
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 descriptor.
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.
.Pp
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.
.Pp
The following callbacks can be defined, cf.
.Fn 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.
.Bl -tag -width "xfdnotfnx"
.It rfb
Read a frame from the file descriptor onto the specified buffer.
.It wfb
Write a frame from the specified buffer into the file descriptor.
.It cmpfb
Identify if a buffer is the response to the specified buffer.
.It gotfb
Called iff no outstanding request matches the incoming frame.
In other words, this is called when we receive a request from a peer.
.It fdnotfn
Receive notifications about a change-of-state in a file descriptor's
status.
.El
.Pp
Better descriptions for each callback are given below.
.Pp
The buffers of
.Nm
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.
.Pp
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.
.Bl -tag -width xxxx
.It Fn puffs_framebuf_make
Create a buffer.
Return the address of the buffer or
.Dv NULL
in case no memory was available.
.It Fn puffs_framebuf_destroy pufbuf
Free memory used by buffer.
.It Fn puffs_framebuf_recycle pufbuf
Reset offsets so that buffer can be reused.
Does not free memory or reallocate memory.
.It Fn puffs_framebuf_reserve_space pufbuf space
Make sure that the buffer has
.Ar 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.
.It Fn puffs_framebuf_putdata pufbuf data dlen
Write
.Ar dlen
amount of data from the address
.Ar data
into the buffer.
Moves the offset cursor forward
.Ar dlen
bytes.
.It Fn puffs_framebuf_putdata_atoff pufbuf offset data dlen
Like
.Fn puffs_framebuf_putdata ,
except writes data at buffer offset
.Ar offset .
It is legal to write past the current end of the buffer.
Does NOT modify the current offset cursor.
.It Fn puffs_framebuf_getdata pufbuf data dlen
Read
.Ar dlen
bytes of data from the buffer into
.Ar data .
Advances the offset cursor.
.It Fn puffs_framebuf_getdata_atoff pufbuf offset data dlen
Read data from buffer position
.Ar offset .
Does NOT modify the offset cursor.
.It Fn puffs_framebuf_telloff pufbuf
Return the offset into the buffer.
.It Fn puffs_framebuf_tellsize pufbuf
Return the maximum offset where data has been written, i.e. buffer size.
.It Fn puffs_framebuf_remaining pufbuf
Distance from current offset to the end of the buffer, i.e. size-offset.
.It Fn puffs_framebuf_seekset pufbuf offset
Set the offset cursor to the position
.Ar offset .
This does NOT modify the buffer size, but reserves at least
enough memory memory for a write to
.Ar offset
and will fail if memory cannot be allocated.
.It Fn puffs_framebuf_getwindow pufbuf offset winp winlen
Get a direct memory window into the buffer starting from
.Ar offset .
The maximum mapped window size will be
.Ar winlen
bytes, but this routine might return a smaller window and the caller
should always check the actual mapped size after the call.
The window is returned in
.Ar winp .
This function not modify the buffer offset, but it DOES set the buffer
size to
.Ar offset +
.Ar winlen
in case that value is greater than the current size.
The window is valid until the next until the next
.Fn puffs_framebuf
call operating on the buffer in question.
.It Fn puffs_framev_enqueue_cc pcc fd pufbuf flags
Add the buffer
.Ar pufbuf
to outgoing queue of descriptor
.Ar fd
and yield with the continuation
.Ar 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.
.Pp
Usually the buffer is placed at the end of the output queue.
However, if
.Ar flags
contains
.Dv PUFFS_FBQUEUE_URGENT ,
.Ar pufbuf
is placed in the front of the queue to be sent immediately after
the current PDU (if any) has been sent.
.It Fn puffs_framev_enqueue_cb pu fd pufbuf fcb fcb_arg flags
Enqueue the buffer
.Ar pufbuf
for outgoing data and immediately return.
Once a response arrives, the callback
.Fn fcb
will be called with the argument
.Ar fcb_arg .
The callback function
.Fn 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.
.Pp
See
.Fn puffs_framev_enqueue_cc
for
.Ar flags .
.It Fn puffs_framev_cb pu pufbuf arg error
Callback function.
Called when a response to a specific request arrives from the server.
If
.Ar error
is non-zero, the framework was unable to obtain a response and the
function should not examine the contents of
.Ar pufbuf ,
only do resource cleanup.
May not block.
.It Fn puffs_framev_enqueue_justsend pu fd pufbuf waitreply flags
Enqueue the buffer
.Ar pufbuf
for outgoing traffic and immediately return.
The parameter
.Ar 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-recoverable error.
.Pp
See
.Fn puffs_framev_enqueue_cc
for
.Ar flags .
.It Fn puffs_framev_enqueue_directsend pcc fd pufbuf flags
Acts like
.Fn puffs_framev_enqueue_justsend
with the exception that the call yields until the frame has been sent.
As opposed to
.Fn puffs_framev_enqueue_cc ,
the routine does not wait for input, but returns immediately after
sending the frame.
.Pp
See
.Fn puffs_framev_enqueue_cc
for
.Ar flags .
.It Fn puffs_framev_enqueue_directreceive pcc fd pufbuf flags
Receive data into
.Ar pufbuf .
This routine yields until a complete frame has been read into
the buffer by the readframe routine.
.Pp
See
.Fn puffs_framev_enqueue_cc
for
.Ar flags .
.It Fn puffs_framev_framebuf_ccpromote pufbuf pcc
Promote the framebuffer
.Ar pufbuf
sent with
.Fn puffs_framev_enqueue_cb
or
.Fn puffs_framev_enqueue_justsend
to a wait using
.Ar pcc
and yield until the result arrives.
The response from the file server for
.Ar pufbuf
must not yet have arrived.
If sent with
.Fn puffs_framev_enqueue_justsend ,
the call must be expecting a response.
.It Fn puffs_framev_enqueue_waitevent pcc fd what
Waits for an event in
.Ar what
to happen on file descriptor
.Ar fd .
The events which happened are returned back in
.Ar what .
The possible events are
.Dv PUFFS_FBIO_READ ,
.Dv PUFFS_FBIO_WRITE ,
and
.Dv PUFFS_FBIO_ERROR ,
specifying read, write and error conditions, respectively.
Error is always checked.
.Pp
This call does not depend on if the events were previously enabled on
the file descriptor - the specified events are always checked
regardless.
.Pp
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.
.It Fn puffs_framev_readframe_fn pu pufbuf fd done
Callback function.
Read at most one frame from file descriptor
.Ar fd
into the buffer
.Ar pufbuf .
If a complete frame is read, the value pointed to by
.Ar 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
.Er 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.
.It Fn puffs_framev_writeframe_fn pu pufbuf fd done
Write the frame contained in
.Ar pufbuf
to the file descriptor
.Ar fd .
In case the entire frame is successfully written,
.Ar *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
.Er 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.
.Pp
It is a good idea to make sure that this function can handle a possible
.Dv SIGPIPE
caused by a closed connection.
For example, the file server can opt to trap
.Dv SIGPIPE
or, if writing to a socket, call
.Fn send
with the flag
.Dv MSG_NOSIGNAL
instead of using
.Fn write .
.It Fn puffs_framev_cmpframe_fn pu pufbuf_cmp1 pufbuf_cmp2 notresp
Compare the file system internal request tags in
.Ar pufbuf_cmp1
and
.Ar 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
.Xr qsort 3 .
If it can be determined from
.Ar pufbuf_cmp1
that it is not a response to any outstanding request,
.Ar notresp
should be set to non-zero.
This will cause
.Nm
to skip the test of the buffer against the rest of the outstanding
request.
May not block.
.It Fn puffs_framev_gotframe_fn pu pufbuf
Called when no outstanding request matches an incoming frame.
The ownership of
.Ar pufbuf
is transferred to the called function and must be destroyed once
processing is over.
May not block.
.It Fn puffs_framev_fdnotify_fn pu fd what
Is called when the read or write side of the file descriptor
.Ar fd
is closed.
It is called once for each side, the bitmask parameter
.Ar what
specified what is currently closed:
.Dv PUFFS_FBIO_READ
and
.Dv PUFFS_FBIO_WRITE
for read and write, respectively.
.It Fn puffs_framev_init pu rfb wfb cmpfb gotfb fdnotfn
Initializes the given callbacks to the system.
They will be used when
.Fn puffs_mainloop
is called.
The framework provides the routines
.Fn puffs_framev_removeonclose
and
.Fn puffs_framev_unmountonclose ,
which can be given as
.Ar fdnotfn .
The first one removes the file descriptor once both sides are closed
while the second one unmounts the file system and exits the mainloop.
.It Fn puffs_framev_addfd pu fd what
Add file descriptor
.Ar fd
to be handled by the framework.
It is legal to add a file descriptor either before calling
.Fn puffs_mainloop
or at time when running.
The parameter
.Ar what
controls enabling of input and output events and can be a bitwise
combination of
.Dv PUFFS_FBIO_READ
and
.Dv PUFFS_FBIO_WRITE .
If not specified, the descriptor will be in a disabled state.
.It Fn puffs_framev_enablefd pu fd what
Enable events of type
.Ar what
for file descriptor
.Ar fd .
.It Fn puffs_framev_disablefd pu fd what
Disable events of type
.Ar what
for file descriptor
.Ar fd .
.It Fn puffs_framev_removefd pu fd error
Remove file descriptor
.Ar 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
.Ar error .
In case 0 is supplied as this parameter,
.Er ECONNRESET
is used.
.Pp
The file system
.Em must
explicitly remove each fd it has added.
A good place to do this is
.Fn puffs_framev_fdnotify_fn
or
.Fn puffs_node_reclaim ,
depending a little on the structure of the file system.
.It Fn puffs_framev_unmountonclose pu fd what
This is library provided convenience routine for
.Fn 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
.Xr mount_psshfs 8
which depend on a single connection.
.El
.Sh CODE REFERENCES
The current users of
.Nm
in the tree are
.Xr mount_psshfs 8
and
.Xr mount_9p 8 .
See
.Pa src/usr.sbin/puffs/mount_psshfs
and
.Pa src/usr.sbin/puffs/mount_9p
for the respective usage examples.
.Sh RETURN VALUES
These functions generally return \-1 to signal error and set
.Er errno
to indicate the type of error.
.Sh SEE ALSO
.Xr puffs 3 ,
.Xr puffs_cc 3 ,
.Xr puffs_ops 3
.Rs
.%A Antti Kantee
.%D September 2007
.%I Helsinki University of Technology
.%R Tech Report TKK-TKO-B157
.%T Using puffs for Implementing Client-Server Distributed File Systems
.Re
.Rs
.%A Antti Kantee
.%D March 2008
.%J Proceedings of AsiaBSDCon 2008
.%P pp. 55-70
.%T Send and Receive of File System Protocols: Userspace Approach With puffs
.Re