[dpdk-dev] [PATCH v2 2/5] mem: add API to obtain memory-backed file info

[Yuanhan Liu]

On Fri, Feb 05, 2016 at 07:20:25PM +0800, Jianfeng Tan wrote:
> A new API named rte_eal_get_backfile_info() and a new data
> struct back_file is added to obstain information of memory-
> backed file info.

I would normally suggest to try hard to find some solution else, instead
of introducing yet another new API, espeically when you just came up with
one user only.

> 
> Signed-off-by: Huawei Xie <huawei.xie at intel.com>
> Signed-off-by: Jianfeng Tan <jianfeng.tan at intel.com>
> ---
>  lib/librte_eal/common/include/rte_memory.h | 16 ++++++++++++
>  lib/librte_eal/linuxapp/eal/eal_memory.c   | 40 +++++++++++++++++++++++++++++-
>  2 files changed, 55 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/librte_eal/common/include/rte_memory.h b/lib/librte_eal/common/include/rte_memory.h
> index 587a25d..b09397e 100644
> --- a/lib/librte_eal/common/include/rte_memory.h
> +++ b/lib/librte_eal/common/include/rte_memory.h
> @@ -109,6 +109,22 @@ struct rte_memseg {
>  } __rte_packed;
>  
>  /**
> + * This struct is used to store information about memory-backed file that
> + * we mapped in memory initialization.
> + */
> +struct back_file {
> +	void *addr;         /**< virtual addr */
> +	size_t size;        /**< the page size */
> +	char filepath[PATH_MAX]; /**< path to backing file on filesystem */
> +};

So, that's all the info you'd like to get. I'm thinking you may don't
need another new API to retrieve them at all:

Say, you can get the filepath and fd from /proc/self/fd (by filtering it
with "rtemap_"):

    $ ls /proc/3487/fd -l
    total 0
    lrwx------ 1 root root 64 Mar  7 20:37 0 -> /dev/pts/2
    lrwx------ 1 root root 64 Mar  7 20:37 1 -> /dev/pts/2
    lrwx------ 1 root root 64 Mar  7 20:37 2 -> /dev/pts/2
    lrwx------ 1 root root 64 Mar  7 20:37 3 -> /run/.rte_config
    lr-x------ 1 root root 64 Mar  7 20:37 4 -> /dev/hugepages
    lr-x------ 1 root root 64 Mar  7 20:37 5 -> /mnt
==> lrwx------ 1 root root 64 Mar  7 20:37 6 -> /dev/hugepages/rtemap_0


Which could also save you an extra "open" at caller side for that
file as well.

And you can get the virtual addr and size from /proc/self/maps:

    $ grep rtemap_ /proc/3487/maps
    7fff40000000-7fffc0000000 rw-s 00000000 00:22 21082 /dev/hugepages/rtemap_0


Will that work for you?

	--yliu