Re: [PATCH v8 1/5] vfio/migration: Add debugfs to live migration driver

[Alex Williamson]

On Fri, 17 Feb 2023 16:48:27 +0800
Longfang Liu <liulongfang@xxxxxxxxxx> wrote:

> There are multiple devices, software and operational steps involved
> in the process of live migration. An error occurred on any node may
> cause the live migration operation to fail.
> This complex process makes it very difficult to locate and analyze
> the cause when the function fails.
> 
> In order to quickly locate the cause of the problem when the
> live migration fails, I added a set of debugfs to the vfio
> live migration driver.
>                                +-------------------------------------------+
>                                |                                           |
>                                |                                           |
>                                |                  QEMU                     |
>                                |                                           |
>                                |                                           |
>                                +---+----------------------------+----------+
>                                    |      ^                     |      ^
>                                    |      |                     |      |
>  +--------+                        |      |                     |      |
>  |  vfio  |                        v      |                     v      |
>  +--------+                     +---------+--+               +---------+--+
>      ^                          |src vfio_dev|               |dst vfio_dev|
>      |                          +--+---------+               +--+---------+
>      |                             |      ^                     |      ^
>      |                             |      |                     |      |
>      |                             v      |                     |      |
>      |  +-----------+         +-----------+----+                |      |
>      +--+<bdf>file_x+<----+---+migration_attr  |                |      |
>      |  +-----------+     |   +----------------+                |      |
>      |                    +---+migration_data  |                |      |
>      |                    |   +----------------+                |      |
>      |                    +---+migration_debug |                |      |
>      |                    |   +----------------+                |      |
>      |                    |   +----------------+                |      |
>      |                    +---+migration_state |                |      |
>      |                        +----------------+                |      |
>      |                                                          |      |
>      |  +-----------+         +----------------+                |      |
>      +--+<bdf>file_y|<----+---+migration_attr  |                |      |
>         +-----------+     |   +----------------+                |      |
>                           +---+migration_data  |                |      |
>                           |   +----------------+<---------------+      |
>                           +---+migration_debug |                       |
>                           |   +----------------+                       |
>                           |   +----------------+                       |
>                           +---+migration_state +-----------------------+
>                               +----------------+
> 
> The entire debugfs directory will be based on the definition of
> the CONFIG_DEBUG_FS macro. If this macro is not enabled, the
> interfaces in vfio.h will be empty definitions, and the creation
> and initialization of the debugfs directory will not be executed.
> 
> debugfs will create a public root directory "vfio" file.
> then create a device <bdf> named file for each live migration device.

dev_name(), it's only <sbdf> for PCI devices.

> First, create a unified state acquisition file of "migration_state"
> in this device directory.
> Then, create your own debugging files independently according to
> the functional requirements of each device.
> 
> Here, HiSilicon accelerator creates three debug files:
> migration_attr: used to obtain the attribute parameters of the
> current live migration device.
> migration_data: used to get the live migration data of the current
> live migration device.
> migration_debug: Used to debug the current live migration device
> through commands.
> 
> The live migration function of the current device can be tested by
> operating the debug files, and the functional status of the equipment
> and software at each stage can be tested step by step without
> performing the complete live migration function. And after the live
> migration is performed, the migration device data of the live migration
> can be obtained through the debug files.
> 
> Signed-off-by: Longfang Liu <liulongfang@xxxxxxxxxx>
> ---
>  drivers/vfio/Makefile       |  2 +-
>  drivers/vfio/vfio.h         | 14 +++++++
>  drivers/vfio/vfio_debugfs.c | 82 +++++++++++++++++++++++++++++++++++++
>  drivers/vfio/vfio_main.c    |  5 +++
>  include/linux/vfio.h        |  8 ++++
>  5 files changed, 110 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/vfio/vfio_debugfs.c
> 
> diff --git a/drivers/vfio/Makefile b/drivers/vfio/Makefile
> index 70e7dcb302ef..1debcff31d30 100644
> --- a/drivers/vfio/Makefile
> +++ b/drivers/vfio/Makefile
> @@ -7,7 +7,7 @@ vfio-y += vfio_main.o \
>  vfio-$(CONFIG_IOMMUFD) += iommufd.o
>  vfio-$(CONFIG_VFIO_CONTAINER) += container.o
>  vfio-$(CONFIG_VFIO_VIRQFD) += virqfd.o
> -
> +vfio-$(CONFIG_DEBUG_FS) += vfio_debugfs.o
>  obj-$(CONFIG_VFIO_IOMMU_TYPE1) += vfio_iommu_type1.o
>  obj-$(CONFIG_VFIO_IOMMU_SPAPR_TCE) += vfio_iommu_spapr_tce.o
>  obj-$(CONFIG_VFIO_PCI) += pci/
> diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
> index e9721d8424bc..66c00f97e9cc 100644
> --- a/drivers/vfio/vfio.h
> +++ b/drivers/vfio/vfio.h
> @@ -258,4 +258,18 @@ static inline void vfio_device_put_kvm(struct vfio_device *device)
>  }
>  #endif
>  
> +#ifdef CONFIG_DEBUG_FS
> +void vfio_debugfs_create_root(void);
> +void vfio_debugfs_remove_root(void);
> +
> +void vfio_vf_debugfs_init(struct vfio_device *vdev);
> +void vfio_vf_debugfs_exit(struct vfio_device *vdev);

s/vf_// throughout.

> +#else
> +static inline void vfio_debugfs_create_root(void) { }
> +static inline void vfio_debugfs_remove_root(void) { }
> +
> +static inline void vfio_vf_debugfs_init(struct vfio_device *vdev) { }
> +static inline void vfio_vf_debugfs_exit(struct vfio_device *vdev) { }
> +#endif /* CONFIG_DEBUG_FS */
> +
>  #endif
> diff --git a/drivers/vfio/vfio_debugfs.c b/drivers/vfio/vfio_debugfs.c
> new file mode 100644
> index 000000000000..c5df1496fe0e
> --- /dev/null
> +++ b/drivers/vfio/vfio_debugfs.c
> @@ -0,0 +1,82 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2023, HiSilicon Ltd.
> + */
> +
> +#include <linux/device.h>
> +#include <linux/debugfs.h>
> +#include <linux/seq_file.h>
> +#include <linux/vfio.h>
> +#include "vfio.h"
> +
> +static struct dentry *vfio_debugfs_root;
> +
> +static int vfio_vf_state_read(struct seq_file *seq, void *data)
> +{
> +	struct device *vf_dev = seq->private;
> +	struct vfio_device *vdev = container_of(vf_dev, struct vfio_device, device);
> +	enum vfio_device_mig_state state;
> +	int ret;
> +
> +	ret = vdev->mig_ops->migration_get_state(vdev, &state);
> +	if (ret) {
> +		dev_err(vf_dev, "failed to get device migration state");

Isn't the errno below sufficient?  No need to add the ability to fill
logs as well.

> +		return -EINVAL;
> +	}
> +
> +	switch (state) {
> +	case VFIO_DEVICE_STATE_RUNNING:
> +		seq_printf(seq, "%s\n", "RUNNING");
> +		break;
> +	case VFIO_DEVICE_STATE_STOP_COPY:
> +		seq_printf(seq, "%s\n", "STOP_COPY");
> +		break;
> +	case VFIO_DEVICE_STATE_STOP:
> +		seq_printf(seq, "%s\n", "STOP");
> +		break;
> +	case VFIO_DEVICE_STATE_RESUMING:
> +		seq_printf(seq, "%s\n", "RESUMING");
> +		break;
> +	case VFIO_DEVICE_STATE_RUNNING_P2P:
> +		seq_printf(seq, "%s\n", "RESUMING_P2P");
> +		break;
> +	case VFIO_DEVICE_STATE_ERROR:
> +		seq_printf(seq, "%s\n", "ERROR");
> +		break;
> +	default:
> +		seq_printf(seq, "%s\n", "Invalid");
> +	}
> +
> +	return 0;
> +}
> +
> +void vfio_vf_debugfs_init(struct vfio_device *vdev)
> +{
> +	struct device *dev = &vdev->device;
> +
> +	vdev->debug_root = debugfs_create_dir(dev_name(vdev->dev), vfio_debugfs_root);
> +
> +	debugfs_create_devm_seqfile(dev, "migration_state", vdev->debug_root,
> +				  vfio_vf_state_read);
> +}
> +EXPORT_SYMBOL_GPL(vfio_vf_debugfs_init);
> +
> +void vfio_vf_debugfs_exit(struct vfio_device *vdev)
> +{
> +	debugfs_remove_recursive(vdev->debug_root);
> +}
> +EXPORT_SYMBOL_GPL(vfio_vf_debugfs_exit);

The above two should probably be vfio_device_debugfs_{init,exit}().

> +
> +void  vfio_debugfs_create_root(void)
> +{
> +	vfio_debugfs_root = debugfs_create_dir("vfio", NULL);
> +}
> +EXPORT_SYMBOL_GPL(vfio_debugfs_create_root);
> +
> +void  vfio_debugfs_remove_root(void)
> +{
> +	debugfs_remove_recursive(vfio_debugfs_root);
> +	vfio_debugfs_root = NULL;
> +}
> +EXPORT_SYMBOL_GPL(vfio_debugfs_remove_root);

As Jason notes, this becomes part of the vfio module, these latter two
don't need to be exported to be called by vfio_main.

Thanks,
Alex

> +
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index 3a597e799918..09772fd3a396 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -1408,6 +1408,9 @@ static int __init vfio_init(void)
>  	}
>  
>  	pr_info(DRIVER_DESC " version: " DRIVER_VERSION "\n");
> +
> +	vfio_debugfs_create_root();
> +
>  	return 0;
>  
>  err_dev_class:
> @@ -1425,6 +1428,8 @@ static void __exit vfio_cleanup(void)
>  	vfio_virqfd_exit();
>  	vfio_group_cleanup();
>  	xa_destroy(&vfio_device_set_xa);
> +
> +	vfio_debugfs_remove_root();
>  }
>  
>  module_init(vfio_init);
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index 93134b023968..fa6b898ebb58 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -63,6 +63,14 @@ struct vfio_device {
>  	struct iommufd_ctx *iommufd_ictx;
>  	bool iommufd_attached;
>  #endif
> +
> +#ifdef CONFIG_DEBUG_FS
> +	/*
> +	 * debug_root is a static property of the vfio_device
> +	 * which must be set prior to registering the vfio_device.
> +	 */
> +	struct dentry *debug_root;
> +#endif
>  };
>  
>  /**