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Date: Wed, 03 Jan 2024 08:57:36 -0800
From: John Fastabend <john.fastabend@gmail.com>
To: Barret Rhoden <brho@google.com>, 
 Andrii Nakryiko <andrii@kernel.org>, 
 Alexei Starovoitov <ast@kernel.org>, 
 Daniel Borkmann <daniel@iogearbox.net>, 
 Song Liu <song@kernel.org>, 
 Yonghong Song <yonghong.song@linux.dev>
Cc: mattbobrowski@google.com, 
 bpf@vger.kernel.org, 
 linux-kernel@vger.kernel.org
Message-ID: <65959200a747b_2384720814@john.notmuch>
In-Reply-To: <20240103153307.553838-2-brho@google.com>
References: <20240103153307.553838-1-brho@google.com>
 <20240103153307.553838-2-brho@google.com>
Subject: RE: [PATCH bpf-next 1/2] libbpf: add helpers for mmapping maps
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Barret Rhoden wrote:
> bpf_map__mmap_size() was internal to bpftool.  Use that to make wrappers
> for mmap and munmap.
> 
> Signed-off-by: Barret Rhoden <brho@google.com>
> ---
>  tools/bpf/bpftool/gen.c  | 16 +++-------------
>  tools/lib/bpf/libbpf.c   | 23 +++++++++++++++++++++++
>  tools/lib/bpf/libbpf.h   |  6 ++++++
>  tools/lib/bpf/libbpf.map |  4 ++++
>  4 files changed, 36 insertions(+), 13 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> index ee3ce2b8000d..a328e960c141 100644
> --- a/tools/bpf/bpftool/gen.c
> +++ b/tools/bpf/bpftool/gen.c
> @@ -453,16 +453,6 @@ static void print_hex(const char *data, int data_sz)
>  	}
>  }
>  
> -static size_t bpf_map_mmap_sz(const struct bpf_map *map)
> -{
> -	long page_sz = sysconf(_SC_PAGE_SIZE);
> -	size_t map_sz;
> -
> -	map_sz = (size_t)roundup(bpf_map__value_size(map), 8) * bpf_map__max_entries(map);
> -	map_sz = roundup(map_sz, page_sz);
> -	return map_sz;
> -}
> -
>  /* Emit type size asserts for all top-level fields in memory-mapped internal maps. */
>  static void codegen_asserts(struct bpf_object *obj, const char *obj_name)
>  {
> @@ -641,7 +631,7 @@ static void codegen_destroy(struct bpf_object *obj, const char *obj_name)
>  		if (bpf_map__is_internal(map) &&
>  		    (bpf_map__map_flags(map) & BPF_F_MMAPABLE))
>  			printf("\tskel_free_map_data(skel->%1$s, skel->maps.%1$s.initial_value, %2$zd);\n",
> -			       ident, bpf_map_mmap_sz(map));
> +			       ident, bpf_map__mmap_size(map));
>  		codegen("\
>  			\n\
>  				skel_closenz(skel->maps.%1$s.map_fd);	    \n\
> @@ -723,7 +713,7 @@ static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *h
>  					goto cleanup;			    \n\
>  				skel->maps.%1$s.initial_value = (__u64) (long) skel->%1$s;\n\
>  			}						    \n\
> -			", ident, bpf_map_mmap_sz(map));
> +			", ident, bpf_map__mmap_size(map));
>  	}
>  	codegen("\
>  		\n\
> @@ -780,7 +770,7 @@ static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *h
>  			if (!skel->%1$s)				    \n\
>  				return -ENOMEM;				    \n\
>  			",
> -		       ident, bpf_map_mmap_sz(map), mmap_flags);
> +		       ident, bpf_map__mmap_size(map), mmap_flags);
>  	}
>  	codegen("\
>  		\n\
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index ebcfb2147fbd..171a977cb5fd 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -9830,6 +9830,29 @@ void *bpf_map__initial_value(struct bpf_map *map, size_t *psize)
>  	return map->mmaped;
>  }

It seems libbpf.c has its own bpf_map_mmap_sz() as well.

 static size_t bpf_map_mmap_sz(unsigned int value_sz, unsigned int max_entries)                  
 {                                                                                
        const long page_sz = sysconf(_SC_PAGE_SIZE);                                         
        size_t map_sz;                                                                                
                                                                                    
        map_sz = (size_t)roundup(value_sz, 8) * max_entries;
        map_sz = roundup(map_sz, page_sz);                                                  
        return map_sz;                                                              
 }  

Can we consolidate these a bit. Seems we don't want/need to
have both bpf_map__mmap_size and bpf_map_mmap_sz() floating
around. 

Should bpf_map__mmap_size just calls bpf_map_mmap_sz with
the correct sz and max_entries?

>  
> +size_t bpf_map__mmap_size(const struct bpf_map *map)
> +{
> +	long page_sz = sysconf(_SC_PAGE_SIZE);
> +	size_t map_sz;
> +
> +	map_sz = (size_t)roundup(bpf_map__value_size(map), 8) *
> +		bpf_map__max_entries(map);
> +	map_sz = roundup(map_sz, page_sz);
> +	return map_sz;
> +}
> +
> +void *bpf_map__mmap(const struct bpf_map *map)
> +{
> +	return mmap(NULL, bpf_map__mmap_size(map),
> +		    PROT_READ | PROT_WRITE, MAP_SHARED,
> +		    bpf_map__fd(map), 0);
> +}
> +
> +int bpf_map__munmap(const struct bpf_map *map, void *addr)
> +{
> +	return munmap(addr, bpf_map__mmap_size(map));
> +}
> +
>  bool bpf_map__is_internal(const struct bpf_map *map)
>  {
>  	return map->libbpf_type != LIBBPF_MAP_UNSPEC;
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 6cd9c501624f..148f4c783ca7 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -996,6 +996,12 @@ LIBBPF_API int bpf_map__set_map_extra(struct bpf_map *map, __u64 map_extra);
>  LIBBPF_API int bpf_map__set_initial_value(struct bpf_map *map,
>  					  const void *data, size_t size);
>  LIBBPF_API void *bpf_map__initial_value(struct bpf_map *map, size_t *psize);
> +/* get the mmappable size of the map */
> +LIBBPF_API size_t bpf_map__mmap_size(const struct bpf_map *map);
> +/* mmap the map */
> +LIBBPF_API void *bpf_map__mmap(const struct bpf_map *map);
> +/* munmap the map at addr */
> +LIBBPF_API int bpf_map__munmap(const struct bpf_map *map, void *addr);
>  
>  /**
>   * @brief **bpf_map__is_internal()** tells the caller whether or not the
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 91c5aef7dae7..9e44de4fbf39 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -411,4 +411,8 @@ LIBBPF_1.3.0 {
>  } LIBBPF_1.2.0;
>  
>  LIBBPF_1.4.0 {
> +	global:
> +		bpf_map__mmap_size;
> +		bpf_map__mmap;
> +		bpf_map__munmap;
>  } LIBBPF_1.3.0;
> -- 
> 2.43.0.472.g3155946c3a-goog
> 
>