On Fri, Jun 24, 2016 at 12:06:01PM +0200, Markus Pargmann wrote:
> From: Michael Grzeschik <m.grzeschik@xxxxxxxxxxxxxx>
>
> Signed-off-by: Michael Grzeschik <m.grzeschik@xxxxxxxxxxxxxx>
> Signed-off-by: Markus Pargmann <mpa@xxxxxxxxxxxxxx>
> ---
> common/state/backend_bucket_direct.c | 55 ++++++++++++++++++++++++++++++++++++
> 1 file changed, 55 insertions(+)
What's the problem this patch tries to solve?
Sascha
>
> diff --git a/common/state/backend_bucket_direct.c b/common/state/backend_bucket_direct.c
> index 08892f001e25..772267f6dc1d 100644
> --- a/common/state/backend_bucket_direct.c
> +++ b/common/state/backend_bucket_direct.c
> @@ -29,6 +29,10 @@ struct state_backend_storage_bucket_direct {
>
> int fd;
>
> + /* Cached data of the last read/write */
> + u8 *current_data;
> + ssize_t current_data_len;
> +
> struct device_d *dev;
> };
>
> @@ -99,6 +103,29 @@ static int state_backend_bucket_direct_read(struct state_backend_storage_bucket
> return 0;
> }
>
> +
> +static int state_backend_bucket_direct_fill_cache(
> + struct state_backend_storage_bucket *bucket)
> +{
> + struct state_backend_storage_bucket_direct *direct =
> + get_bucket_direct(bucket);
> + ssize_t read_len;
> + uint8_t *buf;
> + int ret;
> +
> + ret = state_backend_bucket_direct_read(bucket, &buf, &read_len);
> + if (ret < 0) {
> + dev_err(direct->dev, "Failed to read from file, %d\n", ret);
> + free(buf);
> + return ret;
> + }
> +
> + direct->current_data = buf;
> + direct->current_data_len = read_len;
> +
> + return 0;
> +}
> +
> static int state_backend_bucket_direct_write(struct state_backend_storage_bucket
> *bucket, const uint8_t * buf,
> ssize_t len)
> @@ -111,6 +138,11 @@ static int state_backend_bucket_direct_write(struct state_backend_storage_bucket
> if (direct->max_size && len > direct->max_size)
> return -E2BIG;
>
> + /* Nothing in cache? Then read to see what is on the device currently */
> + if (!direct->current_data) {
> + state_backend_bucket_direct_fill_cache(bucket);
> + }
> +
> ret = lseek(direct->fd, direct->offset, SEEK_SET);
> if (ret < 0) {
> dev_err(direct->dev, "Failed to seek file, %d\n", ret);
> @@ -119,6 +151,26 @@ static int state_backend_bucket_direct_write(struct state_backend_storage_bucket
>
> meta.magic = direct_magic;
> meta.written_length = len;
> +
> + /*
> + * If we would write the same data that is currently on the device, we
> + * can return successfully without writing.
> + * Note that the cache may still be empty if the storage is empty or
> + * errors occured.
> + */
> + if (direct->current_data) {
> + dev_dbg(direct->dev, "Comparing cached data, writing %zd bytes, cached %zd bytes\n",
> + len, direct->current_data_len);
> + if (len == direct->current_data_len &&
> + !memcmp(direct->current_data, buf, len)) {
> + dev_dbg(direct->dev, "Data already on device, not writing again\n");
> + return ret;
> + } else {
> + free(direct->current_data);
> + direct->current_data = NULL;
> + }
> + }
> +
> ret = write_full(direct->fd, &meta, sizeof(meta));
> if (ret < 0) {
> dev_err(direct->dev, "Failed to write metadata to file, %d\n", ret);
> @@ -147,6 +199,9 @@ static void state_backend_bucket_direct_free(struct
> struct state_backend_storage_bucket_direct *direct =
> get_bucket_direct(bucket);
>
> + if (direct->current_data)
> + free(direct->current_data);
> +
> close(direct->fd);
> free(direct);
> }
> --
> 2.8.1
>
>
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