linux-kernel - [RFC PATCH 18/20] famfs: Support character dax via the dev_dax

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Message-Id: <fa06095b6a05a26a0a016768b2e2b70663163eeb.1708709155.git.john@groves.net>
Date: Fri, 23 Feb 2024 11:42:02 -0600
From: John Groves <John@...ves.net>
To: John Groves <jgroves@...ron.com>,
	Jonathan Corbet <corbet@....net>,
	Dan Williams <dan.j.williams@...el.com>,
	Vishal Verma <vishal.l.verma@...el.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Jan Kara <jack@...e.cz>,
	Matthew Wilcox <willy@...radead.org>,
	linux-cxl@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	nvdimm@...ts.linux.dev
Cc: John@...ves.net,
	john@...alactic.com,
	Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>,
	dave.hansen@...ux.intel.com,
	gregory.price@...verge.com,
	John Groves <john@...ves.net>
Subject: [RFC PATCH 18/20] famfs: Support character dax via the dev_dax_iomap patch

This commit introduces the ability to open a character /dev/dax device
instead of a block /dev/pmem device. This rests on the dev_dax_iomap
patches earlier in this series.

Signed-off-by: John Groves <john@...ves.net>
---
 fs/famfs/famfs_inode.c | 97 +++++++++++++++++++++++++++++++++++++-----
 1 file changed, 87 insertions(+), 10 deletions(-)

diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
index 0d659820e8ff..7d65ac497147 100644
--- a/fs/famfs/famfs_inode.c
+++ b/fs/famfs/famfs_inode.c
@@ -215,6 +215,93 @@ static const struct super_operations famfs_ops = {
 	.show_options	= famfs_show_options,
 };
 
+/*****************************************************************************/
+
+#if defined(CONFIG_DEV_DAX_IOMAP)
+
+/*
+ * famfs dax_operations  (for char dax)
+ */
+static int
+famfs_dax_notify_failure(struct dax_device *dax_dev, u64 offset,
+			u64 len, int mf_flags)
+{
+	pr_err("%s: offset %lld len %llu flags %x\n", __func__,
+	       offset, len, mf_flags);
+	return -EOPNOTSUPP;
+}
+
+static const struct dax_holder_operations famfs_dax_holder_ops = {
+	.notify_failure		= famfs_dax_notify_failure,
+};
+
+/*****************************************************************************/
+
+/**
+ * famfs_open_char_device()
+ *
+ * Open a /dev/dax device. This only works in kernels with the dev_dax_iomap patch
+ */
+static int
+famfs_open_char_device(
+	struct super_block *sb,
+	struct fs_context  *fc)
+{
+	struct famfs_fs_info *fsi = sb->s_fs_info;
+	struct dax_device    *dax_devp;
+	struct inode         *daxdev_inode;
+
+	int rc = 0;
+
+	pr_notice("%s: Opening character dax device %s\n", __func__, fc->source);
+
+	fsi->dax_filp = filp_open(fc->source, O_RDWR, 0);
+	if (IS_ERR(fsi->dax_filp)) {
+		pr_err("%s: failed to open dax device %s\n",
+		       __func__, fc->source);
+		fsi->dax_filp = NULL;
+		return PTR_ERR(fsi->dax_filp);
+	}
+
+	daxdev_inode = file_inode(fsi->dax_filp);
+	dax_devp     = inode_dax(daxdev_inode);
+	if (IS_ERR(dax_devp)) {
+		pr_err("%s: unable to get daxdev from inode for %s\n",
+		       __func__, fc->source);
+		rc = -ENODEV;
+		goto char_err;
+	}
+
+	rc = fs_dax_get(dax_devp, fsi, &famfs_dax_holder_ops);
+	if (rc) {
+		pr_info("%s: err attaching famfs_dax_holder_ops\n", __func__);
+		goto char_err;
+	}
+
+	fsi->bdev_handle = NULL;
+	fsi->dax_devp = dax_devp;
+
+	return 0;
+
+char_err:
+	filp_close(fsi->dax_filp, NULL);
+	return rc;
+}
+
+#else /* CONFIG_DEV_DAX_IOMAP */
+static int
+famfs_open_char_device(
+	struct super_block *sb,
+	struct fs_context  *fc)
+{
+	pr_err("%s: Root device is %s, but your kernel does not support famfs on /dev/dax\n",
+	       __func__, fc->source);
+	return -ENODEV;
+}
+
+
+#endif /* CONFIG_DEV_DAX_IOMAP */
+
 /***************************************************************************************
  * dax_holder_operations for block dax
  */
@@ -236,16 +323,6 @@ const struct dax_holder_operations famfs_blk_dax_holder_ops = {
 	.notify_failure		= famfs_blk_dax_notify_failure,
 };
 
-static int
-famfs_open_char_device(
-	struct super_block *sb,
-	struct fs_context  *fc)
-{
-	pr_err("%s: Root device is %s, but your kernel does not support famfs on /dev/dax\n",
-	       __func__, fc->source);
-	return -ENODEV;
-}
-
 /**
  * famfs_open_device()
  *
-- 
2.43.0