Re: [RFC 01/16] blkcg:Introduce blkio.app_identifier knob to blkio controller

Daniel Wagner
2020-08-04T11:31:36Z

Hi,

[cc Tejun]

On Tue, Aug 04, 2020 at 07:43:01AM +0530, Muneendra wrote:
> This Patch added a unique application identifier i.e
> blkio.app_identifier knob to blkio controller which
> allows identification of traffic sources at an
> individual cgroup based Applications
> (ex:virtual machine (VM))level in both host and
> fabric infrastructure.

Is there any specific reason the commit message is formatted in this
way? It looks a bit strange not using a bit more of horizontal space.

> Also provided an interface blkcg_get_app_identifier to
> grab the app identifier associated with a bio.
>
> Added a sysfs interface blkio.app_identifier to get/set the appid.
>
> This capability can be utilized by multiple block transport infrastructure
> like fc,iscsi,roce ..
>
> Signed-off-by: Muneendra <muneendra.kumar@broadcom.com>
> ---
> block/blk-cgroup.c | 32 ++++++++++++++++++++++++++++++++
> include/linux/blk-cgroup.h | 19 +++++++++++++++++++
> 2 files changed, 51 insertions(+)
>
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index 0ecc897b225c..697eccb3ba7a 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -492,6 +492,33 @@ static int blkcg_reset_stats(struct cgroup_subsys_state *css,
> return 0;
> }
>
> +static int blkcg_read_appid(struct seq_file *sf, void *v)
> +{
> + struct blkcg *blkcg = css_to_blkcg(seq_css(sf));
> +
> + seq_printf(sf, "%s\n", blkcg->app_identifier);
> + return 0;
> +}
> +
> +static ssize_t blkcg_write_appid(struct kernfs_open_file *of,
> + char *buf, size_t nbytes, loff_t off)
> +{
> + struct cgroup_subsys_state *css = of_css(of);
> + struct blkcg *blkcg = css_to_blkcg(css);
> + struct blkcg_gq *blkg;
> + int i;
> +
> + buf = strstrip(buf);
> + if (blkcg) {
> + if (nbytes < APPID_LEN)
> + strlcpy(blkcg->app_identifier, buf, nbytes);

strstrip() shortens the string but you still copy nbytes.

> + else
> + return -EINVAL;
> + }
> + return nbytes;
> +}
> +
> +
> const char *blkg_dev_name(struct blkcg_gq *blkg)
> {
> /* some drivers (floppy) instantiate a queue w/o disk registered */
> @@ -844,6 +871,11 @@ static struct cftype blkcg_legacy_files[] = {
> .name = "reset_stats",
> .write_u64 = blkcg_reset_stats,
> },
> + {
> + .name = "app_identifier",
> + .write = blkcg_write_appid,
> + .seq_show = blkcg_read_appid,
> + },

I am no expert with cgroups. Isn't this just adding it to cgroup v1 only?

> { } /* terminate */
> };
>
> diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
> index a57ebe2f00ab..3676d7ebb19f 100644
> --- a/include/linux/blk-cgroup.h
> +++ b/include/linux/blk-cgroup.h
> @@ -30,6 +30,7 @@
>
> /* Max limits for throttle policy */
> #define THROTL_IOPS_MAX UINT_MAX
> +#define APPID_LEN 128
>
> #ifdef CONFIG_BLK_CGROUP
>
> @@ -55,6 +56,7 @@ struct blkcg {
> struct blkcg_policy_data *cpd[BLKCG_MAX_POLS];
>
> struct list_head all_blkcgs_node;
> + char app_identifier[APPID_LEN];
> #ifdef CONFIG_CGROUP_WRITEBACK
> struct list_head cgwb_list;
> #endif
> @@ -239,6 +241,23 @@ static inline struct blkcg *css_to_blkcg(struct cgroup_subsys_state *css)
> return css ? container_of(css, struct blkcg, css) : NULL;
> }
>
> +/**
> + * blkcg_get_app_identifier - grab the app identifier associated with a bio
> + * @bio: target bio
> + *
> + * This returns the app identifier associated with a bio,
> + * %NULL if not associated.
> + * Callers are expected to either handle %NULL or know association has been
> + * done prior to calling this.
> + */
> +static inline char *blkcg_get_app_identifier(struct bio *bio)
> +{
> + if (bio && (bio->bi_blkg) &&
> + (strlen(bio->bi_blkg->blkcg->app_identifier)))
> + return bio->bi_blkg->blkcg->app_identifier;

Too many brackets

Thanks,
Daniel