linux-kernel - [PATCH 03/13] kernfs: add support for get_unmapped

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Message-Id: <20251220040446.274991-4-houtao@huaweicloud.com>
Date: Sat, 20 Dec 2025 12:04:36 +0800
From: Hou Tao <houtao@...weicloud.com>
To: linux-kernel@...r.kernel.org
Cc: linux-pci@...r.kernel.org,
	linux-mm@...ck.org,
	linux-nvme@...ts.infradead.org,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Logan Gunthorpe <logang@...tatee.com>,
	Alistair Popple <apopple@...dia.com>,
	Leon Romanovsky <leonro@...dia.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Tejun Heo <tj@...nel.org>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...nel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Keith Busch <kbusch@...nel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Christoph Hellwig <hch@....de>,
	Sagi Grimberg <sagi@...mberg.me>,
	houtao1@...wei.com
Subject: [PATCH 03/13] kernfs: add support for get_unmapped_area callback

From: Hou Tao <houtao1@...wei.com>

kernfs has already support ->mmap callback, however it doesn't support
->get_unmapped_area callback to return PMD-aligned or PUD-aligned
virtual address. The following patch will need it to support compound
page for p2pdma device memory, therefore add the necessary support for it.

When the ->get_unmapped_area callback is not defined in kernfs_ops or
the callback returns -EOPNOTSUPP, kernfs_get_unmapped_area() will
fallback to mm_get_unmapped_area().

Signed-off-by: Hou Tao <houtao1@...wei.com>
---
 fs/kernfs/file.c       | 37 +++++++++++++++++++++++++++++++++++++
 include/linux/kernfs.h |  3 +++
 2 files changed, 40 insertions(+)

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 9adf36e6364b..9773b5734a2c 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -454,6 +454,39 @@ static const struct vm_operations_struct kernfs_vm_ops = {
 	.access		= kernfs_vma_access,
 };
 
+static unsigned long kernfs_get_unmapped_area(struct file *file, unsigned long uaddr,
+					      unsigned long len, unsigned long pgoff,
+					      unsigned long flags)
+{
+	struct kernfs_open_file *of = kernfs_of(file);
+	const struct kernfs_ops *ops;
+	long addr;
+
+	if (!(of->kn->flags & KERNFS_HAS_MMAP))
+		return -ENODEV;
+
+	mutex_lock(&of->mutex);
+
+	addr = -ENODEV;
+	if (!kernfs_get_active_of(of))
+		goto out_unlock;
+
+	ops = kernfs_ops(of->kn);
+	if (ops->get_unmapped_area) {
+		addr = ops->get_unmapped_area(of, uaddr, len, pgoff, flags);
+		if (!IS_ERR_VALUE(addr) || addr != -EOPNOTSUPP)
+			goto out_put;
+	}
+	addr = mm_get_unmapped_area(file, uaddr, len, pgoff, flags);
+
+out_put:
+	kernfs_put_active_of(of);
+out_unlock:
+	mutex_unlock(&of->mutex);
+
+	return addr;
+}
+
 static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma)
 {
 	struct kernfs_open_file *of = kernfs_of(file);
@@ -1017,6 +1050,7 @@ const struct file_operations kernfs_file_fops = {
 	.write_iter	= kernfs_fop_write_iter,
 	.llseek		= kernfs_fop_llseek,
 	.mmap		= kernfs_fop_mmap,
+	.get_unmapped_area = kernfs_get_unmapped_area,
 	.open		= kernfs_fop_open,
 	.release	= kernfs_fop_release,
 	.poll		= kernfs_fop_poll,
@@ -1052,6 +1086,9 @@ struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
 	unsigned flags;
 	int rc;
 
+	if (ops->get_unmapped_area && !ops->mmap)
+		return ERR_PTR(-EINVAL);
+
 	flags = KERNFS_FILE;
 
 	kn = kernfs_new_node(parent, name, (mode & S_IALLUGO) | S_IFREG,
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index b5a5f32fdfd1..9467b0a2b339 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -324,6 +324,9 @@ struct kernfs_ops {
 
 	int (*mmap)(struct kernfs_open_file *of, struct vm_area_struct *vma);
 	loff_t (*llseek)(struct kernfs_open_file *of, loff_t offset, int whence);
+	unsigned long (*get_unmapped_area)(struct kernfs_open_file *of, unsigned long uaddr,
+					   unsigned long len, unsigned long pgoff,
+					   unsigned long flags);
 };
 
 /*
-- 
2.29.2