linux-kernel - [PATCH v2 14/16] fs/proc: add the proc_mmap

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Message-ID: <832f0563f133b62853f900cf9b5e934b3ee73a7c.1757534913.git.lorenzo.stoakes@oracle.com>
Date: Wed, 10 Sep 2025 21:22:09 +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>,
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Subject: [PATCH v2 14/16] fs/proc: add the proc_mmap_prepare hook for procfs

By adding this hook we enable procfs implementations to be able to use the
.mmap_prepare hook rather than the deprecated .mmap one.

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         | 12 +++++++++---
 include/linux/proc_fs.h |  1 +
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 129490151be1..609abbc84bf4 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -414,9 +414,15 @@ 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,
+	};
+
+	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..e5f65ebd62b8 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -47,6 +47,7 @@ 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 *);
 	unsigned long (*proc_get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
 } __randomize_layout;
 
-- 
2.51.0