[PATCH 1/3] memfd: export alloc_file()

[Pratyush Yadav <pratyush@kernel.org>]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

The Live Update Orchestrator's (LUO) memfd preservation works by
preserving all the folios of a memfd, re-creating an empty memfd on the
next boot, and then inserting back the preserved folios.

Currently it creates the file by directly calling shmem_file_setup().
This leaves out other work done by alloc_file() like setting up the file
mode, flags, or calling the security hooks.

Export alloc_file() to let memfd_luo use it. Rename it to
memfd_alloc_file() since it is no longer private and thus needs a
subsystem prefix.

Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---
 include/linux/memfd.h | 6 ++++++
 mm/memfd.c            | 4 ++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/include/linux/memfd.h b/include/linux/memfd.h
index cc74de3dbcfe..c328a7b356d0 100644
--- a/include/linux/memfd.h
+++ b/include/linux/memfd.h
@@ -17,6 +17,7 @@ struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx);
  * to by vm_flags_ptr.
  */
 int memfd_check_seals_mmap(struct file *file, vm_flags_t *vm_flags_ptr);
+struct file *memfd_alloc_file(const char *name, unsigned int flags);
 #else
 static inline long memfd_fcntl(struct file *f, unsigned int c, unsigned int a)
 {
@@ -31,6 +32,11 @@ static inline int memfd_check_seals_mmap(struct file *file,
 {
 	return 0;
 }
+
+static inline struct file *memfd_alloc_file(const char *name, unsigned int flags)
+{
+	return ERR_PTR(-EINVAL);
+}
 #endif
 
 #endif /* __LINUX_MEMFD_H */
diff --git a/mm/memfd.c b/mm/memfd.c
index ab5312aff14b..f032c6052926 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -456,7 +456,7 @@ static char *alloc_name(const char __user *uname)
 	return ERR_PTR(error);
 }
 
-static struct file *alloc_file(const char *name, unsigned int flags)
+struct file *memfd_alloc_file(const char *name, unsigned int flags)
 {
 	unsigned int *file_seals;
 	struct file *file;
@@ -520,5 +520,5 @@ SYSCALL_DEFINE2(memfd_create,
 		return PTR_ERR(name);
 
 	fd_flags = (flags & MFD_CLOEXEC) ? O_CLOEXEC : 0;
-	return FD_ADD(fd_flags, alloc_file(name, flags));
+	return FD_ADD(fd_flags, memfd_alloc_file(name, flags));
 }
-- 
2.52.0.457.g6b5491de43-goog