[PATCH 07/10] mm/filemap: introduce generic_file_*_mmap_prepare() helpers

[Lorenzo Stoakes]

Since commit c84bf6dd2b83 ("mm: introduce new .mmap_prepare() file
callback"), the f_op->mmap() hook has been deprecated in favour of
f_op->mmap_prepare().

The generic mmap handlers are very simple, so we can very easily convert
these in advance of converting file systems which use them.

This patch does so.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoa...@oracle.com>
---
 include/linux/fs.h |  6 ++++--
 mm/filemap.c       | 29 +++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 7120f80255b3..65cffc445fcc 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3395,8 +3395,10 @@ extern void inode_add_lru(struct inode *inode);
 extern int sb_set_blocksize(struct super_block *, int);
 extern int sb_min_blocksize(struct super_block *, int);
 
-extern int generic_file_mmap(struct file *, struct vm_area_struct *);
-extern int generic_file_readonly_mmap(struct file *, struct vm_area_struct *);
+int generic_file_mmap(struct file *, struct vm_area_struct *);
+int generic_file_mmap_prepare(struct vm_area_desc *desc);
+int generic_file_readonly_mmap(struct file *, struct vm_area_struct *);
+int generic_file_readonly_mmap_prepare(struct vm_area_desc *desc);
 extern ssize_t generic_write_checks(struct kiocb *, struct iov_iter *);
 int generic_write_checks_count(struct kiocb *iocb, loff_t *count);
 extern int generic_write_check_limits(struct file *file, loff_t pos,
diff --git a/mm/filemap.c b/mm/filemap.c
index 93fbc2ef232a..e75608cbf420 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3847,6 +3847,18 @@ int generic_file_mmap(struct file *file, struct 
vm_area_struct *vma)
        return 0;
 }
 
+int generic_file_mmap_prepare(struct vm_area_desc *desc)
+{
+       struct file *file = desc->file;
+       struct address_space *mapping = file->f_mapping;
+
+       if (!mapping->a_ops->read_folio)
+               return -ENOEXEC;
+       file_accessed(file);
+       desc->vm_ops = &generic_file_vm_ops;
+       return 0;
+}
+
 /*
  * This is for filesystems which do not implement ->writepage.
  */
@@ -3856,6 +3868,13 @@ int generic_file_readonly_mmap(struct file *file, struct 
vm_area_struct *vma)
                return -EINVAL;
        return generic_file_mmap(file, vma);
 }
+
+int generic_file_readonly_mmap_prepare(struct vm_area_desc *desc)
+{
+       if (is_shared_maywrite(desc->vm_flags))
+               return -EINVAL;
+       return generic_file_mmap_prepare(desc);
+}
 #else
 vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf)
 {
@@ -3865,15 +3884,25 @@ int generic_file_mmap(struct file *file, struct 
vm_area_struct *vma)
 {
        return -ENOSYS;
 }
+int generic_file_mmap_prepare(struct vm_area_desc *desc)
+{
+       return -ENOSYS;
+}
 int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
 {
        return -ENOSYS;
 }
+int generic_file_readonly_mmap_prepare(struct vm_area_desc *desc)
+{
+       return -ENOSYS;
+}
 #endif /* CONFIG_MMU */
 
 EXPORT_SYMBOL(filemap_page_mkwrite);
 EXPORT_SYMBOL(generic_file_mmap);
+EXPORT_SYMBOL(generic_file_mmap_prepare);
 EXPORT_SYMBOL(generic_file_readonly_mmap);
+EXPORT_SYMBOL(generic_file_readonly_mmap_prepare);
 
 static struct folio *do_read_cache_folio(struct address_space *mapping,
                pgoff_t index, filler_t filler, struct file *file, gfp_t gfp)
-- 
2.49.0