linux-kernel - Re: [PATCH bpf-next 1/5] bpf: Implement task local storage

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Message-ID: <20201028012206.zsa3udr7rqqe3q7y@kafai-mbp>
Date:   Tue, 27 Oct 2020 18:22:06 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     KP Singh <kpsingh@...omium.org>
CC:     <linux-kernel@...r.kernel.org>, <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Paul Turner <pjt@...gle.com>, Jann Horn <jannh@...gle.com>,
        Hao Luo <haoluo@...gle.com>
Subject: Re: [PATCH bpf-next 1/5] bpf: Implement task local storage

On Tue, Oct 27, 2020 at 06:03:13PM +0100, KP Singh wrote:
[ ... ] 

> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index e6ceac3f7d62..bb443c4f3637 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -157,6 +157,7 @@ enum bpf_map_type {
>  	BPF_MAP_TYPE_STRUCT_OPS,
>  	BPF_MAP_TYPE_RINGBUF,
>  	BPF_MAP_TYPE_INODE_STORAGE,
> +	BPF_MAP_TYPE_TASK_STORAGE,
>  };
>  
>  /* Note that tracing related programs such as
> @@ -3742,6 +3743,42 @@ union bpf_attr {
>   * 	Return
>   * 		The helper returns **TC_ACT_REDIRECT** on success or
>   * 		**TC_ACT_SHOT** on error.
> + *
> + * void *bpf_task_storage_get(struct bpf_map *map, void *task, void *value, u64 flags)
After peeking patch 2,  I think the pointer type should be
"struct task_struct *task" instead of "void *task".

Same for bpf_task_storage_delete().

> + *	Description
> + *		Get a bpf_local_storage from the *task*.
> + *
> + *		Logically, it could be thought of as getting the value from
> + *		a *map* with *task* as the **key**.  From this
> + *		perspective,  the usage is not much different from
> + *		**bpf_map_lookup_elem**\ (*map*, **&**\ *task*) except this
> + *		helper enforces the key must be an task_struct and the map must also
> + *		be a **BPF_MAP_TYPE_TASK_STORAGE**.
> + *
> + *		Underneath, the value is stored locally at *task* instead of
> + *		the *map*.  The *map* is used as the bpf-local-storage
> + *		"type". The bpf-local-storage "type" (i.e. the *map*) is
> + *		searched against all bpf_local_storage residing at *task*.
> + *
> + *		An optional *flags* (**BPF_LOCAL_STORAGE_GET_F_CREATE**) can be
> + *		used such that a new bpf_local_storage will be
> + *		created if one does not exist.  *value* can be used
> + *		together with **BPF_LOCAL_STORAGE_GET_F_CREATE** to specify
> + *		the initial value of a bpf_local_storage.  If *value* is
> + *		**NULL**, the new bpf_local_storage will be zero initialized.
> + *	Return
> + *		A bpf_local_storage pointer is returned on success.
> + *
> + *		**NULL** if not found or there was an error in adding
> + *		a new bpf_local_storage.
> + *
> + * int bpf_task_storage_delete(struct bpf_map *map, void *task)
> + *	Description
> + *		Delete a bpf_local_storage from a *task*.
> + *	Return
> + *		0 on success.
> + *
> + *		**-ENOENT** if the bpf_local_storage cannot be found.
>   */