From 9ee6e52616a3231a34236220fb901675fda40291 Mon Sep 17 00:00:00 2001 From: "Lorenzo Stoakes (ARM)" Date: Sat, 26 Sep 2026 11:41:06 +0100 Subject: [PATCH] mm: move drivers/char/mem.c to mm/char-mem.c The memory character driver implements several mm-specific features and is always compiled into the kernel, so move it to mm/ where it belongs. Among other things the driver implements /dev/mem which provides raw access to physical memory, and /dev/zero which either allows mapping of a shmem region (if mapped with MAP_SHARED) or, uniquely, anonymous memory (if mapped MAP_PRIVATE). This change lays the foundations to allow MAP_PRIVATE-/dev/zero to be mapped precisely the same as anonymous memory is mapped as currently it is an edge case within mm. Also update a couple of comments that reference 'drivers/char/mem.c' to reference 'mm/char-mem.c'. Link: https://lore.kernel.org/20260926-map-private-dev-zero-v3-1-d4781e84ccfc@kernel.org Signed-off-by: Lorenzo Stoakes (ARM) Signed-off-by: Andrew Morton Acked-by: David Hildenbrand (Arm) Acked-by: Mike Rapoport (Microsoft) Cc: Arnd Bergmann Cc: Greg Kroah-Hartman Cc: Liam R. Howlett Cc: Vlastimil Babka Cc: Jann Horn Cc: Pedro Falcato Cc: Suren Baghdasaryan Cc: Michal Hocko Cc: Hugh Dickins Cc: Baolin Wang Cc: Matthew Wilcox (Oracle) Cc: Jan Kara --- MAINTAINERS | 4 ++-- drivers/char/Makefile | 2 +- mm/Makefile | 3 ++- drivers/char/mem.c => mm/char-mem.c | 2 +- mm/shmem.c | 2 +- 5 files changed, 7 insertions(+), 6 deletions(-) rename drivers/char/mem.c => mm/char-mem.c (99%) diff --git a/MAINTAINERS b/MAINTAINERS index 7235a92ff879..a7ff3349a524 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -17269,7 +17269,7 @@ F: Documentation/ABI/testing/sysfs-kernel-mm-cma F: Documentation/ABI/testing/sysfs-kernel-mm-numa F: Documentation/admin-guide/mm/ F: Documentation/mm/ -F: drivers/char/mem.c +F: mm/char-mem.c F: include/linux/cma.h F: include/linux/dmapool.h F: include/linux/ioremap.h @@ -17493,7 +17493,7 @@ L: linux-mm@kvack.org S: Maintained W: http://www.linux-mm.org T: git git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm -F: drivers/char/mem.c +F: mm/char-mem.c F: include/trace/events/mmap.h F: fs/proc/task_mmu.c F: fs/proc/task_nommu.c diff --git a/drivers/char/Makefile b/drivers/char/Makefile index a46d7bf7c4c8..bb3bf66937b3 100644 --- a/drivers/char/Makefile +++ b/drivers/char/Makefile @@ -3,7 +3,7 @@ # Makefile for the kernel character device drivers. # -obj-y += mem.o random.o +obj-y += random.o obj-$(CONFIG_TTY_PRINTK) += ttyprintk.o obj-y += misc.o obj-$(CONFIG_TEST_MISC_MINOR) += misc_minor_kunit.o diff --git a/mm/Makefile b/mm/Makefile index e7245cb88c66..2a3ec53d62ee 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -55,7 +55,8 @@ obj-y := filemap.o mempool.o oom_kill.o fadvise.o \ mm_init.o percpu.o slab_common.o \ compaction.o show_mem.o \ interval_tree.o list_lru.o workingset.o \ - debug.o gup.o mmap_lock.o vma_init.o $(mmu-y) + debug.o gup.o mmap_lock.o vma_init.o char-mem.o \ + $(mmu-y) # Give 'page_alloc' its own module-parameter namespace page-alloc-y := page_alloc.o diff --git a/drivers/char/mem.c b/mm/char-mem.c similarity index 99% rename from drivers/char/mem.c rename to mm/char-mem.c index 5b93c92c2cf1..3cc48054a66e 100644 --- a/drivers/char/mem.c +++ b/mm/char-mem.c @@ -1,6 +1,6 @@ // SPDX-License-Identifier: GPL-2.0 /* - * linux/drivers/char/mem.c + * mm/char-mem.c * * Copyright (C) 1991, 1992 Linus Torvalds * diff --git a/mm/shmem.c b/mm/shmem.c index 84f0a2eb85fe..05bc7c3aa525 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2984,7 +2984,7 @@ unsigned long shmem_get_unmapped_area(struct file *file, sb = file_inode(file)->i_sb; } else { /* - * Called directly from mm/mmap.c, or drivers/char/mem.c + * Called directly from mm/mmap.c, or mm/char-mem.c * for "/dev/zero", to create a shared anonymous object. */ if (IS_ERR(shm_mnt))