[PATCH 2/8] mdev: increase netlink buffer sizes

[Denys Vlasenko]

Applied, thank you

On Mon, Dec 16, 2019 at 10:57 PM Jan Klötzke <jan at kloetzke.net> wrote:
>
> The socket receive buffer turned out to be too small for real world
> systems. Use the same size as udevd to be on the safe side. As this is
> just a limit and the memory is not allocated by the kernel until really
> needed there is actually no memory wasted.
>
> Signed-off-by: Jan Klötzke <jan at kloetzke.net>
> ---
>  util-linux/mdev.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/util-linux/mdev.c b/util-linux/mdev.c
> index 207a112c1..4e3299d22 100644
> --- a/util-linux/mdev.c
> +++ b/util-linux/mdev.c
> @@ -1155,9 +1155,21 @@ static void initial_scan(char *temp)
>
>  #if ENABLE_FEATURE_MDEV_DAEMON
>
> -/* uevent applet uses 16k buffer, and mmaps it before every read */
> -# define BUFFER_SIZE (2 * 1024)
> -# define RCVBUF (2 * 1024 * 1024)
> +/*
> + * The kernel (as of v5.4) will pass up to 32 environment variables with a
> + * total of 2kiB on each event. On top of that the action string and device
> + * path are added. Using a 3kiB buffer for the event should suffice in any
> + * case.
> + *
> + * As far as the socket receive buffer size is concerned 2MiB proved to be too
> + * small (see [1]). Udevd seems to use a whooping 128MiB. The socket receive
> + * buffer size is just a resource limit. The buffers are allocated lazily so
> + * the memory is not wasted.
> + *
> + * [1] http://lists.busybox.net/pipermail/busybox/2019-December/087665.html
> + */
> +# define BUFFER_SIZE (3 * 1024)
> +# define RCVBUF (128 * 1024 * 1024)
>  # define MAX_ENV 32
>
>  static void daemon_loop(char *temp, int fd)
> --
> 2.20.1
>
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