Re: [PATCH v2] kernel/ucounts: expose count of inotify watches in use

[Albert Vaca Cintora]

On Fri, Feb 1, 2019 at 9:42 PM Albert Vaca Cintora <albertvaka@xxxxxxxxx> wrote:
>
> Adds a readonly 'current_inotify_watches' entry to the user sysctl table.
> The handler for this entry is a custom function that ends up calling
> proc_dointvec. Said sysctl table already contains 'max_inotify_watches'
> and it gets mounted under /proc/sys/user/.
>
> Inotify watches are a finite resource, in a similar way to available file
> descriptors. The motivation for this patch is to be able to set up
> monitoring and alerting before an application starts failing because
> it runs out of inotify watches.
>
> Signed-off-by: Albert Vaca Cintora <albertvaka@xxxxxxxxx>
> Acked-by: Jan Kara <jack@xxxxxxx>
> Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>

Friendly ping. Any comments on this?

> ---
>  kernel/ucount.c | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
>
> diff --git a/kernel/ucount.c b/kernel/ucount.c
> index f48d1b6376a4..d8b11e53f098 100644
> --- a/kernel/ucount.c
> +++ b/kernel/ucount.c
> @@ -57,6 +57,11 @@ static struct ctl_table_root set_root = {
>         .permissions = set_permissions,
>  };
>
> +#ifdef CONFIG_INOTIFY_USER
> +int proc_read_inotify_watches(struct ctl_table *table, int write,
> +                    void __user *buffer, size_t *lenp, loff_t *ppos);
> +#endif
> +
>  static int zero = 0;
>  static int int_max = INT_MAX;
>  #define UCOUNT_ENTRY(name)                             \
> @@ -79,6 +84,12 @@ static struct ctl_table user_table[] = {
>  #ifdef CONFIG_INOTIFY_USER
>         UCOUNT_ENTRY("max_inotify_instances"),
>         UCOUNT_ENTRY("max_inotify_watches"),
> +       {
> +               .procname       = "current_inotify_watches",
> +               .maxlen         = sizeof(int),
> +               .mode           = 0444,
> +               .proc_handler   = proc_read_inotify_watches,
> +       },
>  #endif
>         { }
>  };
> @@ -226,6 +237,24 @@ void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
>         put_ucounts(ucounts);
>  }
>
> +#ifdef CONFIG_INOTIFY_USER
> +int proc_read_inotify_watches(struct ctl_table *table, int write,
> +                    void __user *buffer, size_t *lenp, loff_t *ppos)
> +{
> +       struct ucounts *ucounts;
> +       struct ctl_table fake_table;
> +       int count;
> +
> +       ucounts = get_ucounts(current_user_ns(), current_euid());
> +       count = atomic_read(&ucounts->ucount[UCOUNT_INOTIFY_WATCHES]);
> +       put_ucounts(ucounts);
> +
> +       fake_table.data = &count;
> +       fake_table.maxlen = sizeof(count);
> +       return proc_dointvec(&fake_table, write, buffer, lenp, ppos);
> +}
> +#endif
> +
>  static __init int user_namespace_sysctl_init(void)
>  {
>  #ifdef CONFIG_SYSCTL
> --
> 2.20.1
>