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SubjectRe: [RFC v3 2/2] kernel/sysctl: support handling command line aliases
On Thu, Mar 26, 2020 at 07:16:06PM +0100, Vlastimil Babka wrote:
> We can now handle sysctl parameters on kernel command line, but historically
> some parameters introduced their own command line equivalent, which we don't
> want to remove for compatibility reasons. We can however convert them to the
> generic infrastructure with a table translating the legacy command line
> parameters to their sysctl names, and removing the one-off param handlers.
>
> This patch adds the support and makes the first conversion to demonstrate it,
> on the (deprecated) numa_zonelist_order parameter.
>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> Changes in v3:
> - constify some things according to Kees
> - expand the comment of sysctl_aliases to note on different timings
>
> fs/proc/proc_sysctl.c | 48 ++++++++++++++++++++++++++++++++++++-------
> mm/page_alloc.c | 9 --------
> 2 files changed, 41 insertions(+), 16 deletions(-)
>
> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> index 8ee3273e4540..3a861e0a7c7e 100644
> --- a/fs/proc/proc_sysctl.c
> +++ b/fs/proc/proc_sysctl.c
> @@ -1729,6 +1729,37 @@ int __init proc_sys_init(void)
>
> struct vfsmount *proc_mnt = NULL;
>
> +struct sysctl_alias {
> + const char *kernel_param;
> + const char *sysctl_param;
> +};
> +
> +/*
> + * Historically some settings had both sysctl and a command line parameter.
> + * With the generic sysctl. parameter support, we can handle them at a single
> + * place and only keep the historical name for compatibility. This is not meant
> + * to add brand new aliases. When adding existing aliases, consider whether
> + * the possibly different moment of changing the value (e.g. from early_param
> + * to the moment do_sysctl_args() is called) is an issue for the specific
> + * parameter.
> + */
> +static const struct sysctl_alias sysctl_aliases[] = {
> + {"numa_zonelist_order", "vm.numa_zonelist_order" },
> + { }
> +};
> +
> +const char *sysctl_find_alias(char *param)

This should be "static" too.

> +{
> + const struct sysctl_alias *alias;
> +
> + for (alias = &sysctl_aliases[0]; alias->kernel_param != NULL; alias++) {
> + if (strcmp(alias->kernel_param, param) == 0)
> + return alias->sysctl_param;
> + }
> +
> + return NULL;
> +}
> +
> /* Set sysctl value passed on kernel command line. */
> static int process_sysctl_arg(char *param, char *val,
> const char *unused, void *arg)
> @@ -1741,15 +1772,18 @@ static int process_sysctl_arg(char *param, char *val,
> loff_t pos = 0;
> ssize_t wret;
>
> - if (strncmp(param, "sysctl", sizeof("sysctl") - 1))
> - return 0;
> -
> - param += sizeof("sysctl") - 1;
> + if (strncmp(param, "sysctl", sizeof("sysctl") - 1) == 0) {
> + param += sizeof("sysctl") - 1;
>
> - if (param[0] != '/' && param[0] != '.')
> - return 0;
> + if (param[0] != '/' && param[0] != '.')
> + return 0;
>
> - param++;
> + param++;
> + } else {
> + param = (char *) sysctl_find_alias(param);
> + if (!param)
> + return 0;
> + }
>
> if (!proc_mnt) {
> proc_fs_type = get_fs_type("proc");
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3c4eb750a199..de7a134b1b8a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5460,15 +5460,6 @@ static int __parse_numa_zonelist_order(char *s)
> return 0;
> }
>
> -static __init int setup_numa_zonelist_order(char *s)
> -{
> - if (!s)
> - return 0;
> -
> - return __parse_numa_zonelist_order(s);
> -}
> -early_param("numa_zonelist_order", setup_numa_zonelist_order);
> -
> char numa_zonelist_order[] = "Node";
>
> /*
> --
> 2.25.1
>

Otherwise, yay, I love it! :)

--
Kees Cook

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