[RFC PATCH v2 11/12] famfs: Introduce mmap and VM fault handling

[John Groves <John@xxxxxxxxxx>]

This commit adds vm_operations, plus famfs_mmap() and fault handlers.
It is still missing iomap_ops, iomap mapping resolution, and
famfs_ioctl() for setting up file-to-memory mappings.

Signed-off-by: John Groves <john@xxxxxxxxxx>
---
 fs/famfs/famfs_file.c | 108 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 106 insertions(+), 2 deletions(-)

diff --git a/fs/famfs/famfs_file.c b/fs/famfs/famfs_file.c
index 48036c71d4ed..585b776dd73c 100644
--- a/fs/famfs/famfs_file.c
+++ b/fs/famfs/famfs_file.c
@@ -16,6 +16,88 @@
 
 #include "famfs_internal.h"
 
+/*********************************************************************
+ * vm_operations
+ */
+static vm_fault_t
+__famfs_filemap_fault(struct vm_fault *vmf, unsigned int pe_size,
+		      bool write_fault)
+{
+	struct inode *inode = file_inode(vmf->vma->vm_file);
+	struct super_block *sb = inode->i_sb;
+	struct famfs_fs_info *fsi = sb->s_fs_info;
+	vm_fault_t ret;
+	pfn_t pfn;
+
+	if (fsi->deverror)
+		return VM_FAULT_SIGBUS;
+
+	if (!IS_DAX(file_inode(vmf->vma->vm_file))) {
+		pr_err("%s: file not marked IS_DAX!!\n", __func__);
+		return VM_FAULT_SIGBUS;
+	}
+
+	if (write_fault) {
+		sb_start_pagefault(inode->i_sb);
+		file_update_time(vmf->vma->vm_file);
+	}
+
+	ret = dax_iomap_fault(vmf, pe_size, &pfn, NULL, NULL /*&famfs_iomap_ops */);
+	if (ret & VM_FAULT_NEEDDSYNC)
+		ret = dax_finish_sync_fault(vmf, pe_size, pfn);
+
+	if (write_fault)
+		sb_end_pagefault(inode->i_sb);
+
+	return ret;
+}
+
+static inline bool
+famfs_is_write_fault(struct vm_fault *vmf)
+{
+	return (vmf->flags & FAULT_FLAG_WRITE) &&
+	       (vmf->vma->vm_flags & VM_SHARED);
+}
+
+static vm_fault_t
+famfs_filemap_fault(struct vm_fault *vmf)
+{
+	return __famfs_filemap_fault(vmf, 0, famfs_is_write_fault(vmf));
+}
+
+static vm_fault_t
+famfs_filemap_huge_fault(struct vm_fault *vmf, unsigned int pe_size)
+{
+	return __famfs_filemap_fault(vmf, pe_size, famfs_is_write_fault(vmf));
+}
+
+static vm_fault_t
+famfs_filemap_page_mkwrite(struct vm_fault *vmf)
+{
+	return __famfs_filemap_fault(vmf, 0, true);
+}
+
+static vm_fault_t
+famfs_filemap_pfn_mkwrite(struct vm_fault *vmf)
+{
+	return __famfs_filemap_fault(vmf, 0, true);
+}
+
+static vm_fault_t
+famfs_filemap_map_pages(struct vm_fault	*vmf, pgoff_t start_pgoff,
+			pgoff_t	end_pgoff)
+{
+	return filemap_map_pages(vmf, start_pgoff, end_pgoff);
+}
+
+const struct vm_operations_struct famfs_file_vm_ops = {
+	.fault		= famfs_filemap_fault,
+	.huge_fault	= famfs_filemap_huge_fault,
+	.map_pages	= famfs_filemap_map_pages,
+	.page_mkwrite	= famfs_filemap_page_mkwrite,
+	.pfn_mkwrite	= famfs_filemap_pfn_mkwrite,
+};
+
 /*********************************************************************
  * file_operations
  */
@@ -25,7 +107,8 @@ static ssize_t
 famfs_file_invalid(struct inode *inode)
 {
 	if (!IS_DAX(inode)) {
-		pr_debug("%s: inode %llx IS_DAX is false\n", __func__, (u64)inode);
+		pr_debug("%s: inode %llx IS_DAX is false\n",
+			 __func__, (u64)inode);
 		return -ENXIO;
 	}
 	return 0;
@@ -101,6 +184,27 @@ famfs_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	return dax_iomap_rw(iocb, from, NULL /*&famfs_iomap_ops*/);
 }
 
+static int
+famfs_file_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	struct inode *inode = file_inode(file);
+	struct super_block *sb = inode->i_sb;
+	struct famfs_fs_info *fsi = sb->s_fs_info;
+	ssize_t rc;
+
+	if (fsi->deverror)
+		return -ENODEV;
+
+	rc = famfs_file_invalid(inode);
+	if (rc)
+		return (int)rc;
+
+	file_accessed(file);
+	vma->vm_ops = &famfs_file_vm_ops;
+	vm_flags_set(vma, VM_HUGEPAGE);
+	return 0;
+}
+
 const struct file_operations famfs_file_operations = {
 	.owner             = THIS_MODULE,
 
@@ -108,7 +212,7 @@ const struct file_operations famfs_file_operations = {
 	.write_iter	   = famfs_dax_write_iter,
 	.read_iter	   = famfs_dax_read_iter,
 	.unlocked_ioctl    = NULL /*famfs_file_ioctl*/,
-	.mmap		   = NULL /* famfs_file_mmap */,
+	.mmap		   = famfs_file_mmap,
 
 	/* Force PMD alignment for mmap */
 	.get_unmapped_area = thp_get_unmapped_area,
-- 
2.43.0