On Wed, Jun 29, 2022 at 04:53:52PM -0600, Khalid Aziz wrote:
Add a ram-based filesystem that contains page table sharing
information and files that enables processes to share page tables.
This patch adds the basic filesystem that can be mounted.
Signed-off-by: Khalid Aziz <khalid.aziz@xxxxxxxxxx>
---
Documentation/filesystems/msharefs.rst | 19 +++++
include/uapi/linux/magic.h | 1 +
mm/Makefile | 2 +-
mm/mshare.c | 103 +++++++++++++++++++++++++
4 files changed, 124 insertions(+), 1 deletion(-)
create mode 100644 Documentation/filesystems/msharefs.rst
create mode 100644 mm/mshare.c
diff --git a/Documentation/filesystems/msharefs.rst b/Documentation/filesystems/msharefs.rst
new file mode 100644
index 000000000000..fd161f67045d
--- /dev/null
+++ b/Documentation/filesystems/msharefs.rst
@@ -0,0 +1,19 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=====================================================
+msharefs - a filesystem to support shared page tables
+=====================================================
+
+msharefs is a ram-based filesystem that allows multiple processes to
+share page table entries for shared pages.
+
+msharefs is typically mounted like this::
+
+ mount -t msharefs none /sys/fs/mshare
+
+When a process calls mshare syscall with a name for the shared address
+range,
You mean creat()?
a file with the same name is created under msharefs with that
+name. This file can be opened by another process, if permissions
+allow, to query the addresses shared under this range. These files are
+removed by mshare_unlink syscall and can not be deleted directly.
Oh?
+Hence these files are created as immutable files.
diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
index f724129c0425..2a57a6ec6f3e 100644
--- a/include/uapi/linux/magic.h
+++ b/include/uapi/linux/magic.h
@@ -105,5 +105,6 @@
#define Z3FOLD_MAGIC 0x33
#define PPC_CMM_MAGIC 0xc7571590
#define SECRETMEM_MAGIC 0x5345434d /* "SECM" */
+#define MSHARE_MAGIC 0x4d534852 /* "MSHR" */
#endif /* __LINUX_MAGIC_H__ */
diff --git a/mm/Makefile b/mm/Makefile
index 6f9ffa968a1a..51a2ab9080d9 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -37,7 +37,7 @@ CFLAGS_init-mm.o += $(call cc-disable-warning, override-init)
CFLAGS_init-mm.o += $(call cc-disable-warning, initializer-overrides)
mmu-y := nommu.o
-mmu-$(CONFIG_MMU) := highmem.o memory.o mincore.o \
+mmu-$(CONFIG_MMU) := highmem.o memory.o mincore.o mshare.o \
mlock.o mmap.o mmu_gather.o mprotect.o mremap.o \
msync.o page_vma_mapped.o pagewalk.o \
pgtable-generic.o rmap.o vmalloc.o
diff --git a/mm/mshare.c b/mm/mshare.c
new file mode 100644
index 000000000000..c8fab3869bab
--- /dev/null
+++ b/mm/mshare.c
Filesystems are usually supposed to live under fs/; is there some reason
to put it in mm/?
I guess shmfs is in mm so maybe this isn't much of an objection.
Also, should this fs be selectable via a Kconfig option?