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SubjectRe: [PATCH v2 4/5] ALSA: xen-front: Implement handling of shared buffers
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On 16/04/18 08:24, Oleksandr Andrushchenko wrote:
> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>
> Implement shared buffer handling according to the
> para-virtualized sound device protocol at xen/interface/io/sndif.h:
> - manage buffer memory
> - handle granted references
> - handle page directories
>
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> ---
> sound/xen/Makefile | 3 +-
> sound/xen/xen_snd_front.c | 8 ++
> sound/xen/xen_snd_front_shbuf.c | 193 ++++++++++++++++++++++++++++++++++++++++
> sound/xen/xen_snd_front_shbuf.h | 36 ++++++++
> 4 files changed, 239 insertions(+), 1 deletion(-)
> create mode 100644 sound/xen/xen_snd_front_shbuf.c
> create mode 100644 sound/xen/xen_snd_front_shbuf.h
>
> diff --git a/sound/xen/Makefile b/sound/xen/Makefile
> index 03c669984000..f028bc30af5d 100644
> --- a/sound/xen/Makefile
> +++ b/sound/xen/Makefile
> @@ -2,6 +2,7 @@
>
> snd_xen_front-objs := xen_snd_front.o \
> xen_snd_front_cfg.o \
> - xen_snd_front_evtchnl.o
> + xen_snd_front_evtchnl.o \
> + xen_snd_front_shbuf.o
>
> obj-$(CONFIG_SND_XEN_FRONTEND) += snd_xen_front.o
> diff --git a/sound/xen/xen_snd_front.c b/sound/xen/xen_snd_front.c
> index eb46bf4070f9..0569c6c596a3 100644
> --- a/sound/xen/xen_snd_front.c
> +++ b/sound/xen/xen_snd_front.c
> @@ -11,6 +11,7 @@
> #include <linux/delay.h>
> #include <linux/module.h>
>
> +#include <xen/page.h>
> #include <xen/platform_pci.h>
> #include <xen/xen.h>
> #include <xen/xenbus.h>
> @@ -186,6 +187,13 @@ static struct xenbus_driver xen_driver = {
>
> static int __init xen_drv_init(void)
> {
> + /* At the moment we only support case with XEN_PAGE_SIZE == PAGE_SIZE */
> + if (XEN_PAGE_SIZE != PAGE_SIZE) {
> + pr_err(XENSND_DRIVER_NAME ": different kernel and Xen page sizes are not supported: XEN_PAGE_SIZE (%lu) != PAGE_SIZE (%lu)\n",
> + XEN_PAGE_SIZE, PAGE_SIZE);
> + return -ENODEV;
> + }

Do you really want to print that error message on bare metal?

> +
> if (!xen_domain())
> return -ENODEV;
>
> diff --git a/sound/xen/xen_snd_front_shbuf.c b/sound/xen/xen_snd_front_shbuf.c
> new file mode 100644
> index 000000000000..6845dbc7fdf5
> --- /dev/null
> +++ b/sound/xen/xen_snd_front_shbuf.c
> @@ -0,0 +1,193 @@
> +// SPDX-License-Identifier: GPL-2.0 OR MIT
> +
> +/*
> + * Xen para-virtual sound device
> + *
> + * Copyright (C) 2016-2018 EPAM Systems Inc.
> + *
> + * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> + */
> +
> +#include <xen/xen.h>
> +#include <xen/xenbus.h>
> +
> +#include "xen_snd_front_shbuf.h"
> +
> +grant_ref_t xen_snd_front_shbuf_get_dir_start(struct xen_snd_front_shbuf *buf)
> +{
> + if (!buf->grefs)
> + return GRANT_INVALID_REF;
> +
> + return buf->grefs[0];
> +}
> +
> +void xen_snd_front_shbuf_clear(struct xen_snd_front_shbuf *buf)
> +{
> + memset(buf, 0, sizeof(*buf));
> +}
> +
> +void xen_snd_front_shbuf_free(struct xen_snd_front_shbuf *buf)
> +{
> + int i;
> +
> + if (buf->grefs) {
> + for (i = 0; i < buf->num_grefs; i++)
> + if (buf->grefs[i] != GRANT_INVALID_REF)
> + gnttab_end_foreign_access(buf->grefs[i],
> + 0, 0UL);
> + kfree(buf->grefs);
> + }
> + kfree(buf->directory);
> + free_pages_exact(buf->buffer, buf->buffer_sz);
> + xen_snd_front_shbuf_clear(buf);
> +}
> +
> +/*
> + * number of grant references a page can hold with respect to the
> + * xensnd_page_directory header
> + */
> +#define XENSND_NUM_GREFS_PER_PAGE ((XEN_PAGE_SIZE - \
> + offsetof(struct xensnd_page_directory, gref)) / \
> + sizeof(grant_ref_t))
> +
> +static void fill_page_dir(struct xen_snd_front_shbuf *buf,
> + int num_pages_dir)
> +{
> + struct xensnd_page_directory *page_dir;
> + unsigned char *ptr;
> + int i, cur_gref, grefs_left, to_copy;
> +
> + ptr = buf->directory;
> + grefs_left = buf->num_grefs - num_pages_dir;
> + /*
> + * skip grant references at the beginning, they are for pages granted
> + * for the page directory itself
> + */
> + cur_gref = num_pages_dir;
> + for (i = 0; i < num_pages_dir; i++) {
> + page_dir = (struct xensnd_page_directory *)ptr;
> + if (grefs_left <= XENSND_NUM_GREFS_PER_PAGE) {
> + to_copy = grefs_left;
> + page_dir->gref_dir_next_page = GRANT_INVALID_REF;
> + } else {
> + to_copy = XENSND_NUM_GREFS_PER_PAGE;
> + page_dir->gref_dir_next_page = buf->grefs[i + 1];
> + }
> +
> + memcpy(&page_dir->gref, &buf->grefs[cur_gref],
> + to_copy * sizeof(grant_ref_t));
> +
> + ptr += XEN_PAGE_SIZE;
> + grefs_left -= to_copy;
> + cur_gref += to_copy;
> + }
> +}
> +
> +static int grant_references(struct xenbus_device *xb_dev,
> + struct xen_snd_front_shbuf *buf,
> + int num_pages_dir, int num_pages_buffer,
> + int num_grefs)
> +{
> + grant_ref_t priv_gref_head;
> + unsigned long frame;
> + int ret, i, j, cur_ref;
> + int otherend_id;
> +
> + ret = gnttab_alloc_grant_references(num_grefs, &priv_gref_head);
> + if (ret)
> + return ret;
> +
> + buf->num_grefs = num_grefs;
> + otherend_id = xb_dev->otherend_id;
> + j = 0;
> +
> + for (i = 0; i < num_pages_dir; i++) {
> + cur_ref = gnttab_claim_grant_reference(&priv_gref_head);
> + if (cur_ref < 0) {
> + ret = cur_ref;
> + goto fail;
> + }
> +
> + frame = xen_page_to_gfn(virt_to_page(buf->directory +
> + XEN_PAGE_SIZE * i));
> + gnttab_grant_foreign_access_ref(cur_ref, otherend_id, frame, 0);
> + buf->grefs[j++] = cur_ref;
> + }
> +
> + for (i = 0; i < num_pages_buffer; i++) {
> + cur_ref = gnttab_claim_grant_reference(&priv_gref_head);
> + if (cur_ref < 0) {
> + ret = cur_ref;
> + goto fail;
> + }
> +
> + frame = xen_page_to_gfn(virt_to_page(buf->buffer +
> + XEN_PAGE_SIZE * i));
> + gnttab_grant_foreign_access_ref(cur_ref, otherend_id, frame, 0);
> + buf->grefs[j++] = cur_ref;
> + }
> +
> + gnttab_free_grant_references(priv_gref_head);
> + fill_page_dir(buf, num_pages_dir);
> + return 0;
> +
> +fail:
> + gnttab_free_grant_references(priv_gref_head);
> + return ret;
> +}
> +
> +static int alloc_int_buffers(struct xen_snd_front_shbuf *buf,
> + int num_pages_dir, int num_pages_buffer,
> + int num_grefs)
> +{
> + buf->grefs = kcalloc(num_grefs, sizeof(*buf->grefs), GFP_KERNEL);
> + if (!buf->grefs)
> + return -ENOMEM;
> +
> + buf->directory = kcalloc(num_pages_dir, XEN_PAGE_SIZE, GFP_KERNEL);
> + if (!buf->directory)
> + goto fail;
> +
> + buf->buffer_sz = num_pages_buffer * XEN_PAGE_SIZE;
> + buf->buffer = alloc_pages_exact(buf->buffer_sz, GFP_KERNEL);
> + if (!buf->buffer)
> + goto fail;
> +
> + return 0;
> +
> +fail:
> + kfree(buf->grefs);
> + buf->grefs = NULL;
> + kfree(buf->directory);

Why do you need to free those here? Shouldn't that be done via
xen_snd_front_shbuf_free() in case of an error?


Juergen

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