[PATCH v4 08/15] s390/vfio-ap: Transition device migration state from STOP to RESUMING

[Anthony Krowiak <akrowiak@linux.ibm.com>]

Transitioning from VFIO_DEVICE_STATE_STOP to VFIO_DEVICE_STATE_RESUMING
starts a process of restoring the device state of the vfio device on the
target system. To prepare for restoring the device state, open a file
stream to receive the guest's AP configuration saved when the device state
on the source system transitioned from VFIO_DEVICE_STATE_STOP to
VFIO_DEVICE_STATE_STOP_COPY.

Note:
This commit introduces the file operations structure for migration state
files with a stub implementation of the write operation. The complete
implementation is provided in the subsequent commit.

This incremental approach allows for easier review of the migration
infrastructure setup separate from the actual implementation logic.

Signed-off-by: Anthony Krowiak <akrowiak@linux.ibm.com>
---
 drivers/s390/crypto/vfio_ap_migration.c | 54 ++++++++++++++++++++++++-
 1 file changed, 52 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/crypto/vfio_ap_migration.c b/drivers/s390/crypto/vfio_ap_migration.c
index 5ef7127b697a..e917cc995d35 100644
--- a/drivers/s390/crypto/vfio_ap_migration.c
+++ b/drivers/s390/crypto/vfio_ap_migration.c
@@ -65,6 +65,17 @@ vfio_ap_release_stop_copy_file(struct vfio_ap_migration_data *mig_data)
 		mig_data->stop_copy_mig_file = NULL;
 }
 
+static void
+vfio_ap_release_resuming_file(struct vfio_ap_migration_data *mig_data)
+{
+	if (mig_data->resuming_mig_state.filp)
+		mig_data->resuming_mig_state.filp = NULL;
+
+	kfree(mig_data->resuming_mig_state.ap_config);
+	mig_data->resuming_mig_state.ap_config = NULL;
+	mig_data->resuming_mig_state.config_sz = 0;
+}
+
 static int vfio_ap_release_mig_file(struct inode *file_inode, struct file *filp)
 {
 	struct ap_matrix_mdev *matrix_mdev = filp->private_data;
@@ -74,6 +85,8 @@ static int vfio_ap_release_mig_file(struct inode *file_inode, struct file *filp)
 
 	if (filp == matrix_mdev->mig_data->stop_copy_mig_file)
 		vfio_ap_release_stop_copy_file(matrix_mdev->mig_data);
+	else if (filp == matrix_mdev->mig_data->resuming_mig_state.filp)
+		vfio_ap_release_resuming_file(matrix_mdev->mig_data);
 	else
 		return -ENOENT;
 
@@ -311,6 +324,32 @@ static struct file *vfio_ap_open_file_stream(struct ap_matrix_mdev *matrix_mdev,
 	return filp;
 }
 
+static ssize_t vfio_ap_resuming_write(struct file *filp, const char __user *buf,
+				      size_t len, loff_t *pos)
+{
+	/* TODO */
+	return -EOPNOTSUPP;
+}
+
+static const struct file_operations vfio_ap_resume_fops = {
+	.owner = THIS_MODULE,
+	.write = vfio_ap_resuming_write,
+	.release = vfio_ap_release_mig_file,
+};
+
+static struct file *vfio_ap_resuming_init(struct ap_matrix_mdev *matrix_mdev)
+{
+	struct vfio_ap_migration_data *mig_data;
+	struct file *filp;
+
+	lockdep_assert_held(&matrix_dev->mdevs_lock);
+
+	mig_data = matrix_mdev->mig_data;
+	filp = vfio_ap_open_file_stream(matrix_mdev, &vfio_ap_resume_fops, O_WRONLY);
+
+	return filp;
+}
+
 static struct file *
 vfio_ap_transition_to_state(struct ap_matrix_mdev *matrix_mdev,
 			    enum vfio_device_mig_state new_state)
@@ -342,10 +381,21 @@ vfio_ap_transition_to_state(struct ap_matrix_mdev *matrix_mdev,
 		return filp;
 	}
 
+	/*
+	 * Begins the process of restoring the vfio device state by creating and
+	 * returning a streaming data_fd to be used to read in the internal
+	 * state of the vfio-ap device on the destination host.
+	 */
 	if (cur_state == VFIO_DEVICE_STATE_STOP &&
 	    new_state == VFIO_DEVICE_STATE_RESUMING) {
-		/* TODO */
-		return ERR_PTR(-EOPNOTSUPP);
+		struct file *filp = vfio_ap_resuming_init(matrix_mdev);
+
+		if (IS_ERR(filp))
+			return ERR_CAST(filp);
+
+		mig_data->resuming_mig_state.filp = filp;
+
+		return filp;
 	}
 
 	if ((cur_state == VFIO_DEVICE_STATE_RESUMING &&
-- 
2.53.0