[RFC PATCH 10/20] famfs: famfs_open_device() & dax_holder_operations

John Groves
2024-02-23T17:42:46Z

Famfs works on both /dev/pmem and /dev/dax devices. This commit introduces
the function that opens a block (pmem) device and the struct
dax_holder_operations that are needed for that ABI.

In this commit, support for opening character /dev/dax is stubbed. A
later commit introduces this capability.

Signed-off-by: John Groves <john@groves.net>
---
fs/famfs/famfs_inode.c | 83 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 83 insertions(+)

diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
index 3329aff000d1..82c861998093 100644
--- a/fs/famfs/famfs_inode.c
+++ b/fs/famfs/famfs_inode.c
@@ -68,5 +68,88 @@ static const struct super_operations famfs_ops = {
.show_options = famfs_show_options,
};

+/***************************************************************************************
+ * dax_holder_operations for block dax
+ */
+
+static int
+famfs_blk_dax_notify_failure(
+ struct dax_device *dax_devp,
+ u64 offset,
+ u64 len,
+ int mf_flags)
+{
+
+ pr_err("%s: dax_devp %llx offset %llx len %lld mf_flags %x\n",
+ __func__, (u64)dax_devp, (u64)offset, (u64)len, mf_flags);
+ return -EOPNOTSUPP;
+}
+
+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()
+ *
+ * Open the memory device. If it looks like /dev/dax, call famfs_open_char_device().
+ * Otherwise try to open it as a block/pmem device.
+ */
+static int
+famfs_open_device(
+ struct super_block *sb,
+ struct fs_context *fc)
+{
+ struct famfs_fs_info *fsi = sb->s_fs_info;
+ struct dax_device *dax_devp;
+ u64 start_off = 0;
+ struct bdev_handle *handlep;
+
+ if (fsi->dax_devp) {
+ pr_err("%s: already mounted\n", __func__);
+ return -EALREADY;
+ }
+
+ if (strstr(fc->source, "/dev/dax")) /* There is probably a better way to check this */
+ return famfs_open_char_device(sb, fc);
+
+ if (!strstr(fc->source, "/dev/pmem")) { /* There is probably a better way to check this */
+ pr_err("%s: primary backing dev (%s) is not pmem\n",
+ __func__, fc->source);
+ return -EINVAL;
+ }
+
+ handlep = bdev_open_by_path(fc->source, FAMFS_BLKDEV_MODE, fsi, &fs_holder_ops);
+ if (IS_ERR(handlep->bdev)) {
+ pr_err("%s: failed blkdev_get_by_path(%s)\n", __func__, fc->source);
+ return PTR_ERR(handlep->bdev);
+ }
+
+ dax_devp = fs_dax_get_by_bdev(handlep->bdev, &start_off,
+ fsi /* holder */,
+ &famfs_blk_dax_holder_ops);
+ if (IS_ERR(dax_devp)) {
+ pr_err("%s: unable to get daxdev from handlep->bdev\n", __func__);
+ bdev_release(handlep);
+ return -ENODEV;
+ }
+ fsi->bdev_handle = handlep;
+ fsi->dax_devp = dax_devp;
+
+ pr_notice("%s: root device is block dax (%s)\n", __func__, fc->source);
+ return 0;
+}
+
+

MODULE_LICENSE("GPL");
--
2.43.0