mm/shmem: introduce shmem_file_setup_with_mnt

We are planning to use our own tmpfs mnt in i915 in place of the
shm_mnt, such that we can control the mount options, in particular
huge=, which we require to support huge-gtt-pages. So rather than roll
our own version of __shmem_file_setup, it would be preferred if we could
just give shmem our mnt, and let it do the rest.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Hugh Dickins <hughd@google.com>
Cc: linux-mm@kvack.org
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171006145041.21673-2-matthew.auld@intel.com
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171006221833.32439-1-chris@chris-wilson.co.uk

include/linux/shmem_fs.h

@@ -53,6 +53,8 @@ extern struct file *shmem_file_setup(const char *name,
 					loff_t size, unsigned long flags);
 extern struct file *shmem_kernel_file_setup(const char *name, loff_t size,
 					    unsigned long flags);
+extern struct file *shmem_file_setup_with_mnt(struct vfsmount *mnt,
+		const char *name, loff_t size, unsigned long flags);
 extern int shmem_zero_setup(struct vm_area_struct *);
 extern unsigned long shmem_get_unmapped_area(struct file *, unsigned long addr,
 		unsigned long len, unsigned long pgoff, unsigned long flags);

mm/shmem.c

@@ -4183,7 +4183,7 @@ static const struct dentry_operations anon_ops = {
 	.d_dname = simple_dname
 };
 
-static struct file *__shmem_file_setup(const char *name, loff_t size,
+static struct file *__shmem_file_setup(struct vfsmount *mnt, const char *name, loff_t size,
 				       unsigned long flags, unsigned int i_flags)
 {
 	struct file *res;
@@ -4192,8 +4192,8 @@ static struct file *__shmem_file_setup(const char *name, loff_t size,
 	struct super_block *sb;
 	struct qstr this;
 
-	if (IS_ERR(shm_mnt))
-		return ERR_CAST(shm_mnt);
+	if (IS_ERR(mnt))
+		return ERR_CAST(mnt);
 
 	if (size < 0 || size > MAX_LFS_FILESIZE)
 		return ERR_PTR(-EINVAL);
@@ -4205,8 +4205,8 @@ static struct file *__shmem_file_setup(const char *name, loff_t size,
 	this.name = name;
 	this.len = strlen(name);
 	this.hash = 0; /* will go */
-	sb = shm_mnt->mnt_sb;
-	path.mnt = mntget(shm_mnt);
+	sb = mnt->mnt_sb;
+	path.mnt = mntget(mnt);
 	path.dentry = d_alloc_pseudo(sb, &this);
 	if (!path.dentry)
 		goto put_memory;
@@ -4251,7 +4251,7 @@ put_path:
  */
 struct file *shmem_kernel_file_setup(const char *name, loff_t size, unsigned long flags)
 {
-	return __shmem_file_setup(name, size, flags, S_PRIVATE);
+	return __shmem_file_setup(shm_mnt, name, size, flags, S_PRIVATE);
 }
 
 /**
@@ -4262,10 +4262,24 @@ struct file *shmem_kernel_file_setup(const char *name, loff_t size, unsigned lon
  */
 struct file *shmem_file_setup(const char *name, loff_t size, unsigned long flags)
 {
-	return __shmem_file_setup(name, size, flags, 0);
+	return __shmem_file_setup(shm_mnt, name, size, flags, 0);
 }
 EXPORT_SYMBOL_GPL(shmem_file_setup);
 
+/**
+ * shmem_file_setup_with_mnt - get an unlinked file living in tmpfs
+ * @mnt: the tmpfs mount where the file will be created
+ * @name: name for dentry (to be seen in /proc/<pid>/maps
+ * @size: size to be set for the file
+ * @flags: VM_NORESERVE suppresses pre-accounting of the entire object size
+ */
+struct file *shmem_file_setup_with_mnt(struct vfsmount *mnt, const char *name,
+				       loff_t size, unsigned long flags)
+{
+	return __shmem_file_setup(mnt, name, size, flags, 0);
+}
+EXPORT_SYMBOL_GPL(shmem_file_setup_with_mnt);
+
 /**
  * shmem_zero_setup - setup a shared anonymous mapping
  * @vma: the vma to be mmapped is prepared by do_mmap_pgoff
@@ -4281,7 +4295,7 @@ int shmem_zero_setup(struct vm_area_struct *vma)
 	 * accessible to the user through its mapping, use S_PRIVATE flag to
 	 * bypass file security, in the same way as shmem_kernel_file_setup().
 	 */
-	file = __shmem_file_setup("dev/zero", size, vma->vm_flags, S_PRIVATE);
+	file = shmem_kernel_file_setup("dev/zero", size, vma->vm_flags);
 	if (IS_ERR(file))
 		return PTR_ERR(file);