linux-kernel - [PATCH] mm: make MEMFD_CREATE into a selectable config option

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Message-Id: <20230630-config-memfd-v1-1-9acc3ae38b5a@weissschuh.net>
Date:   Fri, 30 Jun 2023 11:08:53 +0200
From:   Thomas Weißschuh <linux@...ssschuh.net>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Willy Tarreau <w@....eu>,
        Zhangjin Wu <falcon@...ylab.org>,
        Thomas Weißschuh <linux@...ssschuh.net>
Subject: [PATCH] mm: make MEMFD_CREATE into a selectable config option

The memfd_create() syscall, enabled by CONFIG_MEMFD_CREATE, is useful on
its own even when not required by CONFIG_TMPFS or CONFIG_HUGETLBFS.

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@...ssschuh.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@...ssschuh.net>