There're several types of system calls for multiplexed I/O. They're used to receive notifications of I/O events. Typically, userspace applications call them against file descriptor to yield CPU. When I/O is enabled on any of the descriptors, a task of the application is rescheduled, then the application execute I/O calls.
This commit adds a common interface for this type of system calls, named as 'waiter'. This is expected to be used with non-blocking file operation and operations on mapped page frame.
Signed-off-by: Takashi Sakamoto o-takashi@sakamocchi.jp --- axfer/Makefile.am | 5 +- axfer/waiter.c | 99 +++++++++++++++++++++++++++++++++ axfer/waiter.h | 54 ++++++++++++++++++ axfer/xfer-libasound-irq-mmap.c | 14 ++++- axfer/xfer-libasound-irq-rw.c | 26 ++++++++- axfer/xfer-libasound.c | 76 +++++++++++++++++++++++++ axfer/xfer-libasound.h | 7 +++ 7 files changed, 277 insertions(+), 4 deletions(-) create mode 100644 axfer/waiter.c create mode 100644 axfer/waiter.h
diff --git a/axfer/Makefile.am b/axfer/Makefile.am index 960811e..e425a28 100644 --- a/axfer/Makefile.am +++ b/axfer/Makefile.am @@ -22,6 +22,7 @@ noinst_HEADERS = \ xfer.h \ xfer-libasound.h \ frame-cache.h + waiter.h
axfer_SOURCES = \ misc.h \ @@ -47,4 +48,6 @@ axfer_SOURCES = \ frame-cache.c \ xfer-libasound-irq-rw.c \ subcmd-transfer.c \ - xfer-libasound-irq-mmap.c + xfer-libasound-irq-mmap.c \ + waiter.h \ + waiter.c diff --git a/axfer/waiter.c b/axfer/waiter.c new file mode 100644 index 00000000..0bc4740 --- /dev/null +++ b/axfer/waiter.c @@ -0,0 +1,99 @@ +// SPDX-License-Identifier: GPL-2.0 +// +// waiter.c - I/O event waiter. +// +// Copyright (c) 2018 Takashi Sakamoto o-takashi@sakamocchi.jp +// +// Licensed under the terms of the GNU General Public License, version 2. + +#include "waiter.h" + +#include <stdlib.h> +#include <string.h> +#include <errno.h> + +#include "misc.h" + +static const char *const waiter_type_labels[] = { + [WAITER_TYPE_DEFAULT] = "default", +}; + +enum waiter_type waiter_type_from_label(const char *label) +{ + int i; + + for (i = 0; i < ARRAY_SIZE(waiter_type_labels); ++i) { + if (!strcmp(waiter_type_labels[i], label)) + return i; + } + + return WAITER_TYPE_DEFAULT; +} + +const char *waiter_label_from_type(enum waiter_type type) +{ + return waiter_type_labels[type]; +} + +int waiter_context_init(struct waiter_context *waiter, + enum waiter_type type, unsigned int pfd_count) +{ + struct { + enum waiter_type type; + const struct waiter_data *waiter; + } entries[] = { + {WAITER_TYPE_COUNT, NULL}, + }; + int i; + + if (pfd_count == 0) + return -EINVAL; + + for (i = 0; i < ARRAY_SIZE(entries); ++i) { + if (entries[i].type == type) + break; + } + if (i == ARRAY_SIZE(entries)) + return -EINVAL; + + waiter->private_data = malloc(entries[i].waiter->private_size); + if (waiter->private_data == NULL) + return -ENOMEM; + memset(waiter->private_data, 0, entries[i].waiter->private_size); + + waiter->type = type; + waiter->ops = &entries[i].waiter->ops; + + waiter->pfds = calloc(pfd_count, sizeof(*waiter->pfds)); + if (waiter->pfds == NULL) + return -ENOMEM; + waiter->pfd_count = pfd_count; + + return 0; +} + +int waiter_context_prepare(struct waiter_context *waiter) +{ + return waiter->ops->prepare(waiter); +} + +int waiter_context_wait_event(struct waiter_context *waiter, + int timeout_msec) +{ + return waiter->ops->wait_event(waiter, timeout_msec); +} + +void waiter_context_release(struct waiter_context *waiter) +{ + waiter->ops->release(waiter); +} + +void waiter_context_destroy(struct waiter_context *waiter) +{ + if (waiter->pfds) + free(waiter->pfds); + waiter->pfd_count = 0; + if (waiter->private_data) + free(waiter->private_data); + waiter->private_data = NULL; +} diff --git a/axfer/waiter.h b/axfer/waiter.h new file mode 100644 index 00000000..17e01cb --- /dev/null +++ b/axfer/waiter.h @@ -0,0 +1,54 @@ +// SPDX-License-Identifier: GPL-2.0 +// +// waiter.h - a header for I/O event waiter. +// +// Copyright (c) 2018 Takashi Sakamoto o-takashi@sakamocchi.jp +// +// Licensed under the terms of the GNU General Public License, version 2. + +#ifndef __ALSA_UTILS_AXFER_WAITER__H_ +#define __ALSA_UTILS_AXFER_WAITER__H_ + +#include <poll.h> + +enum waiter_type { + WAITER_TYPE_DEFAULT = 0, + WAITER_TYPE_COUNT, +}; + +struct waiter_ops; + +struct waiter_context { + enum waiter_type type; + const struct waiter_ops *ops; + void *private_data; + + struct pollfd *pfds; + unsigned int pfd_count; +}; + +enum waiter_type waiter_type_from_label(const char *label); +const char *waiter_label_from_type(enum waiter_type type); + +int waiter_context_init(struct waiter_context *waiter, + enum waiter_type type, unsigned int pfd_count); +int waiter_context_prepare(struct waiter_context *waiter); +int waiter_context_wait_event(struct waiter_context *waiter, + int timeout_msec); +void waiter_context_release(struct waiter_context *waiter); +void waiter_context_destroy(struct waiter_context *waiter); + +// For internal use in 'waiter' module. + +struct waiter_ops { + int (*prepare)(struct waiter_context *waiter); + int (*wait_event)(struct waiter_context *waiter, int timeout_msec); + void (*release)(struct waiter_context *waiter); +}; + +struct waiter_data { + struct waiter_ops ops; + unsigned int private_size; +}; + +#endif diff --git a/axfer/xfer-libasound-irq-mmap.c b/axfer/xfer-libasound-irq-mmap.c index 18f6dfe..0c96ee5 100644 --- a/axfer/xfer-libasound-irq-mmap.c +++ b/axfer/xfer-libasound-irq-mmap.c @@ -82,10 +82,22 @@ static int irq_mmap_process_frames(struct libasound_state *state, int err;
if (state->use_waiter) { + unsigned short revents; + // Wait for hardware IRQ when no avail space in buffer. - err = snd_pcm_wait(state->handle, -1); + err = xfer_libasound_wait_event(state, -1, &revents); if (err < 0) return err; + if (revents & POLLERR) { + // TODO: error reporting? + return -EIO; + } + if (!(revents & (POLLIN | POLLOUT))) + return -EAGAIN; + + // When rescheduled, current position of data transmission was + // queried to actual hardware by a handler of IRQ. No need to + // perform it; e.g. ioctl(2) with SNDRV_PCM_IOCTL_HWSYNC. }
// Sync cache in user space to data in kernel space to calculate avail diff --git a/axfer/xfer-libasound-irq-rw.c b/axfer/xfer-libasound-irq-rw.c index 625c095..cf4155f 100644 --- a/axfer/xfer-libasound-irq-rw.c +++ b/axfer/xfer-libasound-irq-rw.c @@ -134,10 +134,21 @@ static int r_process_frames_nonblocking(struct libasound_state *state, }
if (state->use_waiter) { + unsigned short revents; + // Wait for hardware IRQ when no available space. - err = snd_pcm_wait(state->handle, -1); + err = xfer_libasound_wait_event(state, -1, &revents); if (err < 0) goto error; + if (revents & POLLERR) { + // TODO: error reporting. + err = -EIO; + goto error; + } + if (!(revents & POLLIN)) { + err = -EAGAIN; + goto error; + } }
// Check available space on the buffer. @@ -289,10 +300,21 @@ static int w_process_frames_nonblocking(struct libasound_state *state, int err;
if (state->use_waiter) { + unsigned short revents; + // Wait for hardware IRQ when no left space. - err = snd_pcm_wait(state->handle, -1); + err = xfer_libasound_wait_event(state, -1, &revents); if (err < 0) goto error; + if (revents & POLLERR) { + // TODO: error reporting. + err = -EIO; + goto error; + } + if (!(revents & POLLOUT)) { + err = -EAGAIN; + goto error; + } }
// Check available space on the buffer. diff --git a/axfer/xfer-libasound.c b/axfer/xfer-libasound.c index a731423..5cef9f1 100644 --- a/axfer/xfer-libasound.c +++ b/axfer/xfer-libasound.c @@ -201,6 +201,7 @@ static int open_handle(struct xfer_context *xfer)
if ((state->nonblock || state->mmap) && !state->test_nowait) state->use_waiter = true; + state->waiter_type = WAITER_TYPE_DEFAULT;
err = snd_pcm_hw_params_any(state->handle, state->hw_params); if (err < 0) @@ -220,6 +221,66 @@ static int open_handle(struct xfer_context *xfer) return set_access_hw_param(state); }
+static int prepare_waiter(struct libasound_state *state) +{ + unsigned int pfd_count; + int err; + + // Nothing to do for dafault waiter (=snd_pcm_wait()). + if (state->waiter_type == WAITER_TYPE_DEFAULT) + return 0; + + err = snd_pcm_poll_descriptors_count(state->handle); + if (err < 0) + return err; + if (err == 0) + return -ENXIO; + pfd_count = (unsigned int)err; + + state->waiter = malloc(sizeof(*state->waiter)); + if (state->waiter == NULL) + return -ENOMEM; + + err = waiter_context_init(state->waiter, state->waiter_type, pfd_count); + if (err < 0) + return err; + + err = snd_pcm_poll_descriptors(state->handle, state->waiter->pfds, + pfd_count); + if (err < 0) + return err; + + return waiter_context_prepare(state->waiter); +} + +int xfer_libasound_wait_event(struct libasound_state *state, int timeout_msec, + unsigned short *revents) +{ + int err; + + if (state->waiter_type != WAITER_TYPE_DEFAULT) { + struct waiter_context *waiter = state->waiter; + + err = waiter_context_wait_event(waiter, timeout_msec); + if (err < 0) + return err; + + err = snd_pcm_poll_descriptors_revents(state->handle, + waiter->pfds, waiter->pfd_count, revents); + } else { + err = snd_pcm_wait(state->handle, timeout_msec); + if (err < 0) + return err; + + if (snd_pcm_stream(state->handle) == SND_PCM_STREAM_PLAYBACK) + *revents = POLLOUT; + else + *revents = POLLIN; + } + + return err; +} + static int configure_hw_params(struct libasound_state *state, snd_pcm_format_t format, unsigned int samples_per_frame, @@ -559,6 +620,21 @@ static int xfer_libasound_pre_process(struct xfer_context *xfer, if (xfer->verbose > 0) snd_pcm_dump(state->handle, state->log);
+ if (state->use_waiter) { + // NOTE: This should be after configuring sw_params due to + // timer descriptor for time-based scheduling model. + err = prepare_waiter(state); + if (err < 0) + return err; + + if (xfer->verbose > 0) { + logging(state, "Waiter type:\n"); + logging(state, + " %s\n", + waiter_label_from_type(state->waiter_type)); + } + } + return 0; }
diff --git a/axfer/xfer-libasound.h b/axfer/xfer-libasound.h index cf940e5..0bcfb40 100644 --- a/axfer/xfer-libasound.h +++ b/axfer/xfer-libasound.h @@ -10,6 +10,7 @@ #define __ALSA_UTILS_AXFER_XFER_LIBASOUND__H_
#include "xfer.h" +#include "waiter.h"
#define logging(state, ...) \ snd_output_printf(state->log, __VA_ARGS__) @@ -49,6 +50,9 @@ struct libasound_state { bool no_softvol:1;
bool use_waiter:1; + + enum waiter_type waiter_type; + struct waiter_context *waiter; };
// For internal use in 'libasound' module. @@ -63,6 +67,9 @@ struct xfer_libasound_ops { unsigned int private_size; };
+int xfer_libasound_wait_event(struct libasound_state *state, int timeout_msec, + unsigned short *revents); + extern const struct xfer_libasound_ops xfer_libasound_irq_rw_ops;
extern const struct xfer_libasound_ops xfer_libasound_irq_mmap_r_ops;