Re: [PATCH] mm: make MEMFD_CREATE into a selectable config option

Darrick J. Wong
2023-06-30T15:33:44Z

On Fri, Jun 30, 2023 at 11:08:53AM +0200, Thomas Weißschuh wrote:
> The memfd_create() syscall, enabled by CONFIG_MEMFD_CREATE, is useful on
> its own even when not required by CONFIG_TMPFS or CONFIG_HUGETLBFS.

If you don't have tmpfs or hugetlbfs enabled, then what fs ends up
backing the file returned by memfd_create()? ramfs?

(Not an objection, I'm just curious...)

--D

> Split it into its own proper bool option that can be enabled by users.
>
> Move that option into mm/ where the code itself also lies.
> Also add "select" statements to CONFIG_TMPFS and CONFIG_HUGETLBFS so
> they automatically enable CONFIG_MEMFD_CREATE as before.
>
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> ---
> fs/Kconfig | 5 ++---
> mm/Kconfig | 3 +++
> 2 files changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/fs/Kconfig b/fs/Kconfig
> index 18d034ec7953..19975b104bc3 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -169,6 +169,7 @@ source "fs/sysfs/Kconfig"
> config TMPFS
> bool "Tmpfs virtual memory file system support (former shm fs)"
> depends on SHMEM
> + select MEMFD_CREATE
> help
> Tmpfs is a file system which keeps all files in virtual memory.
>
> @@ -240,6 +241,7 @@ config HUGETLBFS
> bool "HugeTLB file system support"
> depends on X86 || IA64 || SPARC64 || ARCH_SUPPORTS_HUGETLBFS || BROKEN
> depends on (SYSFS || SYSCTL)
> + select MEMFD_CREATE
> help
> hugetlbfs is a filesystem backing for HugeTLB pages, based on
> ramfs. For architectures that support it, say Y here and read
> @@ -264,9 +266,6 @@ config HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON
> enable HVO by default. It can be disabled via hugetlb_free_vmemmap=off
> (boot command line) or hugetlb_optimize_vmemmap (sysctl).
>
> -config MEMFD_CREATE
> - def_bool TMPFS || HUGETLBFS
> -
> config ARCH_HAS_GIGANTIC_PAGE
> bool
>
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 09130434e30d..22acffd9009d 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1144,6 +1144,9 @@ config KMAP_LOCAL_NON_LINEAR_PTE_ARRAY
> config IO_MAPPING
> bool
>
> +config MEMFD_CREATE
> + bool "Enable memfd_create() system call" if EXPERT
> +
> config SECRETMEM
> default y
> bool "Enable memfd_secret() system call" if EXPERT
>
> ---
> base-commit: e55e5df193d247a38a5e1ac65a5316a0adcc22fa
> change-id: 20230629-config-memfd-be6af03b7dca
>
> Best regards,
> --
> Thomas Weißschuh <linux@weissschuh.net>
>