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qemu/include/io/channel.h
Eric Blake e8ffaa3110 io: Add new qio_channel_read{, v}_all_eof functions 
Some callers want to distinguish between clean EOF (no bytes read)
vs. a short read (at least one byte read, but EOF encountered
before reaching the desired length), as it allows clients the
ability to do a graceful shutdown when a server shuts down at
defined safe points in the protocol, rather than treating all
shutdown scenarios as an error due to EOF.  However, we don't want
to require all callers to have to check for early EOF.  So add
another wrapper function that can be used by the callers that care
about the distinction.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20170905191114.5959-3-eblake@redhat.com>
Acked-by: Daniel P. Berrange <berrange@redhat.com>
2017-09-06 10:11:54 -05:00

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/*
* QEMU I/O channels
*
* Copyright (c) 2015 Red Hat, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, see <http://www.gnu.org/licenses/>.
*
*/
#ifndef QIO_CHANNEL_H
#define QIO_CHANNEL_H
#include "qemu-common.h"
#include "qom/object.h"
#include "qemu/coroutine.h"
#include "block/aio.h"
#define TYPE_QIO_CHANNEL "qio-channel"
#define QIO_CHANNEL(obj) \
OBJECT_CHECK(QIOChannel, (obj), TYPE_QIO_CHANNEL)
#define QIO_CHANNEL_CLASS(klass) \
OBJECT_CLASS_CHECK(QIOChannelClass, klass, TYPE_QIO_CHANNEL)
#define QIO_CHANNEL_GET_CLASS(obj) \
OBJECT_GET_CLASS(QIOChannelClass, obj, TYPE_QIO_CHANNEL)
typedef struct QIOChannel QIOChannel;
typedef struct QIOChannelClass QIOChannelClass;
#define QIO_CHANNEL_ERR_BLOCK -2
typedef enum QIOChannelFeature QIOChannelFeature;
enum QIOChannelFeature {
QIO_CHANNEL_FEATURE_FD_PASS,
QIO_CHANNEL_FEATURE_SHUTDOWN,
QIO_CHANNEL_FEATURE_LISTEN,
};
typedef enum QIOChannelShutdown QIOChannelShutdown;
enum QIOChannelShutdown {
QIO_CHANNEL_SHUTDOWN_BOTH,
QIO_CHANNEL_SHUTDOWN_READ,
QIO_CHANNEL_SHUTDOWN_WRITE,
};
typedef gboolean (*QIOChannelFunc)(QIOChannel *ioc,
GIOCondition condition,
gpointer data);
/**
* QIOChannel:
*
* The QIOChannel defines the core API for a generic I/O channel
* class hierarchy. It is inspired by GIOChannel, but has the
* following differences
*
* - Use QOM to properly support arbitrary subclassing
* - Support use of iovecs for efficient I/O with multiple blocks
* - None of the character set translation, binary data exclusively
* - Direct support for QEMU Error object reporting
* - File descriptor passing
*
* This base class is abstract so cannot be instantiated. There
* will be subclasses for dealing with sockets, files, and higher
* level protocols such as TLS, WebSocket, etc.
*/
struct QIOChannel {
Object parent;
unsigned int features; /* bitmask of QIOChannelFeatures */
char *name;
AioContext *ctx;
Coroutine *read_coroutine;
Coroutine *write_coroutine;
#ifdef _WIN32
HANDLE event; /* For use with GSource on Win32 */
#endif
};
/**
* QIOChannelClass:
*
* This class defines the contract that all subclasses
* must follow to provide specific channel implementations.
* The first five callbacks are mandatory to support, others
* provide additional optional features.
*
* Consult the corresponding public API docs for a description
* of the semantics of each callback
*/
struct QIOChannelClass {
ObjectClass parent;
/* Mandatory callbacks */
ssize_t (*io_writev)(QIOChannel *ioc,
const struct iovec *iov,
size_t niov,
int *fds,
size_t nfds,
Error **errp);
ssize_t (*io_readv)(QIOChannel *ioc,
const struct iovec *iov,
size_t niov,
int **fds,
size_t *nfds,
Error **errp);
int (*io_close)(QIOChannel *ioc,
Error **errp);
GSource * (*io_create_watch)(QIOChannel *ioc,
GIOCondition condition);
int (*io_set_blocking)(QIOChannel *ioc,
bool enabled,
Error **errp);
/* Optional callbacks */
int (*io_shutdown)(QIOChannel *ioc,
QIOChannelShutdown how,
Error **errp);
void (*io_set_cork)(QIOChannel *ioc,
bool enabled);
void (*io_set_delay)(QIOChannel *ioc,
bool enabled);
off_t (*io_seek)(QIOChannel *ioc,
off_t offset,
int whence,
Error **errp);
void (*io_set_aio_fd_handler)(QIOChannel *ioc,
AioContext *ctx,
IOHandler *io_read,
IOHandler *io_write,
void *opaque);
};
/* General I/O handling functions */
/**
* qio_channel_has_feature:
* @ioc: the channel object
* @feature: the feature to check support of
*
* Determine whether the channel implementation supports
* the optional feature named in @feature.
*
* Returns: true if supported, false otherwise.
*/
bool qio_channel_has_feature(QIOChannel *ioc,
QIOChannelFeature feature);
/**
* qio_channel_set_feature:
* @ioc: the channel object
* @feature: the feature to set support for
*
* Add channel support for the feature named in @feature.
*/
void qio_channel_set_feature(QIOChannel *ioc,
QIOChannelFeature feature);
/**
* qio_channel_set_name:
* @ioc: the channel object
* @name: the name of the channel
*
* Sets the name of the channel, which serves as an aid
* to debugging. The name is used when creating GSource
* watches for this channel.
*/
void qio_channel_set_name(QIOChannel *ioc,
const char *name);
/**
* qio_channel_readv_full:
* @ioc: the channel object
* @iov: the array of memory regions to read data into
* @niov: the length of the @iov array
* @fds: pointer to an array that will received file handles
* @nfds: pointer filled with number of elements in @fds on return
* @errp: pointer to a NULL-initialized error object
*
* Read data from the IO channel, storing it in the
* memory regions referenced by @iov. Each element
* in the @iov will be fully populated with data
* before the next one is used. The @niov parameter
* specifies the total number of elements in @iov.
*
* It is not required for all @iov to be filled with
* data. If the channel is in blocking mode, at least
* one byte of data will be read, but no more is
* guaranteed. If the channel is non-blocking and no
* data is available, it will return QIO_CHANNEL_ERR_BLOCK
*
* If the channel has passed any file descriptors,
* the @fds array pointer will be allocated and
* the elements filled with the received file
* descriptors. The @nfds pointer will be updated
* to indicate the size of the @fds array that
* was allocated. It is the callers responsibility
* to call close() on each file descriptor and to
* call g_free() on the array pointer in @fds.
*
* It is an error to pass a non-NULL @fds parameter
* unless qio_channel_has_feature() returns a true
* value for the QIO_CHANNEL_FEATURE_FD_PASS constant.
*
* Returns: the number of bytes read, or -1 on error,
* or QIO_CHANNEL_ERR_BLOCK if no data is available
* and the channel is non-blocking
*/
ssize_t qio_channel_readv_full(QIOChannel *ioc,
const struct iovec *iov,
size_t niov,
int **fds,
size_t *nfds,
Error **errp);
/**
* qio_channel_writev_full:
* @ioc: the channel object
* @iov: the array of memory regions to write data from
* @niov: the length of the @iov array
* @fds: an array of file handles to send
* @nfds: number of file handles in @fds
* @errp: pointer to a NULL-initialized error object
*
* Write data to the IO channel, reading it from the
* memory regions referenced by @iov. Each element
* in the @iov will be fully sent, before the next
* one is used. The @niov parameter specifies the
* total number of elements in @iov.
*
* It is not required for all @iov data to be fully
* sent. If the channel is in blocking mode, at least
* one byte of data will be sent, but no more is
* guaranteed. If the channel is non-blocking and no
* data can be sent, it will return QIO_CHANNEL_ERR_BLOCK
*
* If there are file descriptors to send, the @fds
* array should be non-NULL and provide the handles.
* All file descriptors will be sent if at least one
* byte of data was sent.
*
* It is an error to pass a non-NULL @fds parameter
* unless qio_channel_has_feature() returns a true
* value for the QIO_CHANNEL_FEATURE_FD_PASS constant.
*
* Returns: the number of bytes sent, or -1 on error,
* or QIO_CHANNEL_ERR_BLOCK if no data is can be sent
* and the channel is non-blocking
*/
ssize_t qio_channel_writev_full(QIOChannel *ioc,
const struct iovec *iov,
size_t niov,
int *fds,
size_t nfds,
Error **errp);
/**
* qio_channel_readv_all_eof:
* @ioc: the channel object
* @iov: the array of memory regions to read data into
* @niov: the length of the @iov array
* @errp: pointer to a NULL-initialized error object
*
* Read data from the IO channel, storing it in the
* memory regions referenced by @iov. Each element
* in the @iov will be fully populated with data
* before the next one is used. The @niov parameter
* specifies the total number of elements in @iov.
*
* The function will wait for all requested data
* to be read, yielding from the current coroutine
* if required.
*
* If end-of-file occurs before any data is read,
* no error is reported; otherwise, if it occurs
* before all requested data has been read, an error
* will be reported.
*
* Returns: 1 if all bytes were read, 0 if end-of-file
* occurs without data, or -1 on error
*/
int qio_channel_readv_all_eof(QIOChannel *ioc,
const struct iovec *iov,
size_t niov,
Error **errp);
/**
* qio_channel_readv_all:
* @ioc: the channel object
* @iov: the array of memory regions to read data into
* @niov: the length of the @iov array
* @errp: pointer to a NULL-initialized error object
*
* Read data from the IO channel, storing it in the
* memory regions referenced by @iov. Each element
* in the @iov will be fully populated with data
* before the next one is used. The @niov parameter
* specifies the total number of elements in @iov.
*
* The function will wait for all requested data
* to be read, yielding from the current coroutine
* if required.
*
* If end-of-file occurs before all requested data
* has been read, an error will be reported.
*
* Returns: 0 if all bytes were read, or -1 on error
*/
int qio_channel_readv_all(QIOChannel *ioc,
const struct iovec *iov,
size_t niov,
Error **errp);
/**
* qio_channel_writev_all:
* @ioc: the channel object
* @iov: the array of memory regions to write data from
* @niov: the length of the @iov array
* @errp: pointer to a NULL-initialized error object
*
* Write data to the IO channel, reading it from the
* memory regions referenced by @iov. Each element
* in the @iov will be fully sent, before the next
* one is used. The @niov parameter specifies the
* total number of elements in @iov.
*
* The function will wait for all requested data
* to be written, yielding from the current coroutine
* if required.
*
* Returns: 0 if all bytes were written, or -1 on error
*/
int qio_channel_writev_all(QIOChannel *ioc,
const struct iovec *iov,
size_t niov,
Error **erp);
/**
* qio_channel_readv:
* @ioc: the channel object
* @iov: the array of memory regions to read data into
* @niov: the length of the @iov array
* @errp: pointer to a NULL-initialized error object
*
* Behaves as qio_channel_readv_full() but does not support
* receiving of file handles.
*/
ssize_t qio_channel_readv(QIOChannel *ioc,
const struct iovec *iov,
size_t niov,
Error **errp);
/**
* qio_channel_writev:
* @ioc: the channel object
* @iov: the array of memory regions to write data from
* @niov: the length of the @iov array
* @errp: pointer to a NULL-initialized error object
*
* Behaves as qio_channel_writev_full() but does not support
* sending of file handles.
*/
ssize_t qio_channel_writev(QIOChannel *ioc,
const struct iovec *iov,
size_t niov,
Error **errp);
/**
* qio_channel_read:
* @ioc: the channel object
* @buf: the memory region to read data into
* @buflen: the length of @buf
* @errp: pointer to a NULL-initialized error object
*
* Behaves as qio_channel_readv_full() but does not support
* receiving of file handles, and only supports reading into
* a single memory region.
*/
ssize_t qio_channel_read(QIOChannel *ioc,
char *buf,
size_t buflen,
Error **errp);
/**
* qio_channel_write:
* @ioc: the channel object
* @buf: the memory regions to send data from
* @buflen: the length of @buf
* @errp: pointer to a NULL-initialized error object
*
* Behaves as qio_channel_writev_full() but does not support
* sending of file handles, and only supports writing from a
* single memory region.
*/
ssize_t qio_channel_write(QIOChannel *ioc,
const char *buf,
size_t buflen,
Error **errp);
/**
* qio_channel_read_all_eof:
* @ioc: the channel object
* @buf: the memory region to read data into
* @buflen: the number of bytes to @buf
* @errp: pointer to a NULL-initialized error object
*
* Reads @buflen bytes into @buf, possibly blocking or (if the
* channel is non-blocking) yielding from the current coroutine
* multiple times until the entire content is read. If end-of-file
* occurs immediately it is not an error, but if it occurs after
* data has been read it will return an error rather than a
* short-read. Otherwise behaves as qio_channel_read().
*
* Returns: 1 if all bytes were read, 0 if end-of-file occurs
* without data, or -1 on error
*/
int qio_channel_read_all_eof(QIOChannel *ioc,
char *buf,
size_t buflen,
Error **errp);
/**
* qio_channel_read_all:
* @ioc: the channel object
* @buf: the memory region to read data into
* @buflen: the number of bytes to @buf
* @errp: pointer to a NULL-initialized error object
*
* Reads @buflen bytes into @buf, possibly blocking or (if the
* channel is non-blocking) yielding from the current coroutine
* multiple times until the entire content is read. If end-of-file
* occurs it will return an error rather than a short-read. Otherwise
* behaves as qio_channel_read().
*
* Returns: 0 if all bytes were read, or -1 on error
*/
int qio_channel_read_all(QIOChannel *ioc,
char *buf,
size_t buflen,
Error **errp);
/**
* qio_channel_write_all:
* @ioc: the channel object
* @buf: the memory region to write data into
* @buflen: the number of bytes to @buf
* @errp: pointer to a NULL-initialized error object
*
* Writes @buflen bytes from @buf, possibly blocking or (if the
* channel is non-blocking) yielding from the current coroutine
* multiple times until the entire content is written. Otherwise
* behaves as qio_channel_write().
*
* Returns: 0 if all bytes were written, or -1 on error
*/
int qio_channel_write_all(QIOChannel *ioc,
const char *buf,
size_t buflen,
Error **errp);
/**
* qio_channel_set_blocking:
* @ioc: the channel object
* @enabled: the blocking flag state
* @errp: pointer to a NULL-initialized error object
*
* If @enabled is true, then the channel is put into
* blocking mode, otherwise it will be non-blocking.
*
* In non-blocking mode, read/write operations may
* return QIO_CHANNEL_ERR_BLOCK if they would otherwise
* block on I/O
*/
int qio_channel_set_blocking(QIOChannel *ioc,
bool enabled,
Error **errp);
/**
* qio_channel_close:
* @ioc: the channel object
* @errp: pointer to a NULL-initialized error object
*
* Close the channel, flushing any pending I/O
*
* Returns: 0 on success, -1 on error
*/
int qio_channel_close(QIOChannel *ioc,
Error **errp);
/**
* qio_channel_shutdown:
* @ioc: the channel object
* @how: the direction to shutdown
* @errp: pointer to a NULL-initialized error object
*
* Shutdowns transmission and/or receiving of data
* without closing the underlying transport.
*
* Not all implementations will support this facility,
* so may report an error. To avoid errors, the
* caller may check for the feature flag
* QIO_CHANNEL_FEATURE_SHUTDOWN prior to calling
* this method.
*
* Returns: 0 on success, -1 on error
*/
int qio_channel_shutdown(QIOChannel *ioc,
QIOChannelShutdown how,
Error **errp);
/**
* qio_channel_set_delay:
* @ioc: the channel object
* @enabled: the new flag state
*
* Controls whether the underlying transport is
* permitted to delay writes in order to merge
* small packets. If @enabled is true, then the
* writes may be delayed in order to opportunistically
* merge small packets into larger ones. If @enabled
* is false, writes are dispatched immediately with
* no delay.
*
* When @enabled is false, applications may wish to
* use the qio_channel_set_cork() method to explicitly
* control write merging.
*
* On channels which are backed by a socket, this
* API corresponds to the inverse of TCP_NODELAY flag,
* controlling whether the Nagle algorithm is active.
*
* This setting is merely a hint, so implementations are
* free to ignore this without it being considered an
* error.
*/
void qio_channel_set_delay(QIOChannel *ioc,
bool enabled);
/**
* qio_channel_set_cork:
* @ioc: the channel object
* @enabled: the new flag state
*
* Controls whether the underlying transport is
* permitted to dispatch data that is written.
* If @enabled is true, then any data written will
* be queued in local buffers until @enabled is
* set to false once again.
*
* This feature is typically used when the automatic
* write coalescing facility is disabled via the
* qio_channel_set_delay() method.
*
* On channels which are backed by a socket, this
* API corresponds to the TCP_CORK flag.
*
* This setting is merely a hint, so implementations are
* free to ignore this without it being considered an
* error.
*/
void qio_channel_set_cork(QIOChannel *ioc,
bool enabled);
/**
* qio_channel_seek:
* @ioc: the channel object
* @offset: the position to seek to, relative to @whence
* @whence: one of the (POSIX) SEEK_* constants listed below
* @errp: pointer to a NULL-initialized error object
*
* Moves the current I/O position within the channel
* @ioc, to be @offset. The value of @offset is
* interpreted relative to @whence:
*
* SEEK_SET - the position is set to @offset bytes
* SEEK_CUR - the position is moved by @offset bytes
* SEEK_END - the position is set to end of the file plus @offset bytes
*
* Not all implementations will support this facility,
* so may report an error.
*
* Returns: the new position on success, (off_t)-1 on failure
*/
off_t qio_channel_io_seek(QIOChannel *ioc,
off_t offset,
int whence,
Error **errp);
/**
* qio_channel_create_watch:
* @ioc: the channel object
* @condition: the I/O condition to monitor
*
* Create a new main loop source that is used to watch
* for the I/O condition @condition. Typically the
* qio_channel_add_watch() method would be used instead
* of this, since it directly attaches a callback to
* the source
*
* Returns: the new main loop source.
*/
GSource *qio_channel_create_watch(QIOChannel *ioc,
GIOCondition condition);
/**
* qio_channel_add_watch:
* @ioc: the channel object
* @condition: the I/O condition to monitor
* @func: callback to invoke when the source becomes ready
* @user_data: opaque data to pass to @func
* @notify: callback to free @user_data
*
* Create a new main loop source that is used to watch
* for the I/O condition @condition. The callback @func
* will be registered against the source, to be invoked
* when the source becomes ready. The optional @user_data
* will be passed to @func when it is invoked. The @notify
* callback will be used to free @user_data when the
* watch is deleted
*
* The returned source ID can be used with g_source_remove()
* to remove and free the source when no longer required.
* Alternatively the @func callback can return a FALSE
* value.
*
* Returns: the source ID
*/
guint qio_channel_add_watch(QIOChannel *ioc,
GIOCondition condition,
QIOChannelFunc func,
gpointer user_data,
GDestroyNotify notify);
/**
* qio_channel_attach_aio_context:
* @ioc: the channel object
* @ctx: the #AioContext to set the handlers on
*
* Request that qio_channel_yield() sets I/O handlers on
* the given #AioContext. If @ctx is %NULL, qio_channel_yield()
* uses QEMU's main thread event loop.
*
* You can move a #QIOChannel from one #AioContext to another even if
* I/O handlers are set for a coroutine. However, #QIOChannel provides
* no synchronization between the calls to qio_channel_yield() and
* qio_channel_attach_aio_context().
*
* Therefore you should first call qio_channel_detach_aio_context()
* to ensure that the coroutine is not entered concurrently. Then,
* while the coroutine has yielded, call qio_channel_attach_aio_context(),
* and then aio_co_schedule() to place the coroutine on the new
* #AioContext. The calls to qio_channel_detach_aio_context()
* and qio_channel_attach_aio_context() should be protected with
* aio_context_acquire() and aio_context_release().
*/
void qio_channel_attach_aio_context(QIOChannel *ioc,
AioContext *ctx);
/**
* qio_channel_detach_aio_context:
* @ioc: the channel object
*
* Disable any I/O handlers set by qio_channel_yield(). With the
* help of aio_co_schedule(), this allows moving a coroutine that was
* paused by qio_channel_yield() to another context.
*/
void qio_channel_detach_aio_context(QIOChannel *ioc);
/**
* qio_channel_yield:
* @ioc: the channel object
* @condition: the I/O condition to wait for
*
* Yields execution from the current coroutine until the condition
* indicated by @condition becomes available. @condition must
* be either %G_IO_IN or %G_IO_OUT; it cannot contain both. In
* addition, no two coroutine can be waiting on the same condition
* and channel at the same time.
*
* This must only be called from coroutine context
*/
void qio_channel_yield(QIOChannel *ioc,
GIOCondition condition);
/**
* qio_channel_wait:
* @ioc: the channel object
* @condition: the I/O condition to wait for
*
* Block execution from the current thread until
* the condition indicated by @condition becomes
* available.
*
* This will enter a nested event loop to perform
* the wait.
*/
void qio_channel_wait(QIOChannel *ioc,
GIOCondition condition);
/**
* qio_channel_set_aio_fd_handler:
* @ioc: the channel object
* @ctx: the AioContext to set the handlers on
* @io_read: the read handler
* @io_write: the write handler
* @opaque: the opaque value passed to the handler
*
* This is used internally by qio_channel_yield(). It can
* be used by channel implementations to forward the handlers
* to another channel (e.g. from #QIOChannelTLS to the
* underlying socket).
*/
void qio_channel_set_aio_fd_handler(QIOChannel *ioc,
AioContext *ctx,
IOHandler *io_read,
IOHandler *io_write,
void *opaque);
#endif /* QIO_CHANNEL_H */
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