linux-kernel - [PATCH 14/16] fs/proc: add proc_mmap_[prepare, complete] hooks for procfs

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Message-ID: <81d1c8ba935dffa6f0a82a5a5ecab6e80f90e6c0.1757329751.git.lorenzo.stoakes@oracle.com>
Date: Mon,  8 Sep 2025 12:10:45 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Jonathan Corbet <corbet@....net>, Matthew Wilcox <willy@...radead.org>,
        Guo Ren <guoren@...nel.org>,
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Subject: [PATCH 14/16] fs/proc: add proc_mmap_[prepare, complete] hooks for procfs

By adding these hooks we enable procfs implementations to be able to use
the .mmap_prepare, .mmap_complete hooks rather than the deprecated .mmap
hook.

We treat this as if it were any other nested mmap hook and utilise the
.mmap_prepare compatibility layer if necessary.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
---
 fs/proc/inode.c         | 13 ++++++++++---
 include/linux/proc_fs.h |  5 +++++
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 129490151be1..d031267e2e4a 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -414,9 +414,16 @@ static long proc_reg_compat_ioctl(struct file *file, unsigned int cmd, unsigned
 
 static int pde_mmap(struct proc_dir_entry *pde, struct file *file, struct vm_area_struct *vma)
 {
-	__auto_type mmap = pde->proc_ops->proc_mmap;
-	if (mmap)
-		return mmap(file, vma);
+	const struct file_operations f_op = {
+		.mmap = pde->proc_ops->proc_mmap,
+		.mmap_prepare = pde->proc_ops->proc_mmap_prepare,
+		.mmap_complete = pde->proc_ops->proc_mmap_complete,
+	};
+
+	if (f_op.mmap)
+		return f_op.mmap(file, vma);
+	else if (f_op.mmap_prepare)
+		return __compat_vma_mmap_prepare(&f_op, file, vma);
 	return -EIO;
 }
 
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index f139377f4b31..3573192f813d 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -47,6 +47,11 @@ struct proc_ops {
 	long	(*proc_compat_ioctl)(struct file *, unsigned int, unsigned long);
 #endif
 	int	(*proc_mmap)(struct file *, struct vm_area_struct *);
+	int	(*proc_mmap_prepare)(struct vm_area_desc *);
+	int	(*proc_mmap_complete)(struct file *, struct vm_area_struct *,
+				      const void *context);
+	void	(*proc_mmap_abort)(const struct file *, const void *vm_private_data,
+				   const void *context);
 	unsigned long (*proc_get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
 } __randomize_layout;
 
-- 
2.51.0