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Subject: Re: [PATCH v15 1/2] vfio/migration: Add debugfs to live migration
 driver
To:     Alex Williamson <alex.williamson@redhat.com>
CC:     <jgg@nvidia.com>, <shameerali.kolothum.thodi@huawei.com>,
        <jonathan.cameron@huawei.com>, <bcreeley@amd.com>,
        <kvm@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linuxarm@openeuler.org>
References: <20230901023606.47587-1-liulongfang@huawei.com>
 <20230901023606.47587-2-liulongfang@huawei.com>
 <20230915150026.06bea533.alex.williamson@redhat.com>
From:   liulongfang <liulongfang@huawei.com>
Message-ID: <d541ba02-a8d1-dc8e-a725-4ee82b0c44bb@huawei.com>
Date:   Fri, 22 Sep 2023 14:19:36 +0800
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On 2023/9/16 5:00, Alex Williamson wrote:
> On Fri, 1 Sep 2023 10:36:05 +0800
> liulongfang <liulongfang@huawei.com> wrote:
> 
>> From: Longfang Liu <liulongfang@huawei.com>
>>
>> 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                     |
>>     |                                           |
>>     |                                           |
>>     +---+----------------------------+----------+
>>         |      ^                     |      ^
>>         |      |                     |      |
>>         |      |                     |      |
>>         v      |                     v      |
>>      +---------+--+               +---------+--+
>>      |src vfio_dev|               |dst vfio_dev|
>>      +--+---------+               +--+---------+
>>         |      ^                     |      ^
>>         |      |                     |      |
>>         v      |                     |      |
>>    +-----------+----+           +-----------+----+
>>    |src dev debugfs |           |dst dev debugfs |
>>    +----------------+           +----------------+
>>
>> 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.
>>
>>    vfio
>>     |
>>     +---<dev_name1>
>>     |    +---migration
>>     |        +--state
>>     |
>>     +---<dev_name2>
>>          +---migration
>>              +--state
>>
>> debugfs will create a public root directory "vfio" file.
>> then create a dev_name() file for each live migration device.
>> First, create a unified state acquisition file of "migration"
>> in this device directory.
>> Then, create a public live migration state lookup file "state"
>> Finally, create a directory file based on the device type,
>> and then create the device's own debugging files under
>> this directory file.
>>
>> Signed-off-by: Longfang Liu <liulongfang@huawei.com>
>> ---
>>  drivers/vfio/Makefile       |  1 +
>>  drivers/vfio/vfio.h         | 14 +++++++
>>  drivers/vfio/vfio_debugfs.c | 80 +++++++++++++++++++++++++++++++++++++
>>  drivers/vfio/vfio_main.c    |  5 ++-
>>  include/linux/vfio.h        |  7 ++++
>>  5 files changed, 106 insertions(+), 1 deletion(-)
>>  create mode 100644 drivers/vfio/vfio_debugfs.c
>>
>> diff --git a/drivers/vfio/Makefile b/drivers/vfio/Makefile
>> index c82ea032d352..7934ac829989 100644
>> --- a/drivers/vfio/Makefile
>> +++ b/drivers/vfio/Makefile
>> @@ -8,6 +8,7 @@ vfio-$(CONFIG_VFIO_GROUP) += group.o
>>  vfio-$(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
>> diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
>> index 307e3f29b527..09b00757d0bb 100644
>> --- a/drivers/vfio/vfio.h
>> +++ b/drivers/vfio/vfio.h
>> @@ -448,4 +448,18 @@ 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_device_debugfs_init(struct vfio_device *vdev);
>> +void vfio_device_debugfs_exit(struct vfio_device *vdev);
>> +#else
>> +static inline void vfio_debugfs_create_root(void) { }
>> +static inline void vfio_debugfs_remove_root(void) { }
>> +
>> +static inline void vfio_device_debugfs_init(struct vfio_device *vdev) { }
>> +static inline void vfio_device_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..cd6c01437475
>> --- /dev/null
>> +++ b/drivers/vfio/vfio_debugfs.c
>> @@ -0,0 +1,80 @@
>> +// 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_device_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)
>> +		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", "RUNNING_P2P");
>> +		break;
>> +	case VFIO_DEVICE_STATE_ERROR:
>> +		seq_printf(seq, "%s\n", "ERROR");
> 
> Please order these the same as enum vfio_device_mig_state, we're also
> missing a couple states, ie. PRE_COPY and PRE_COPY_P2P.  Can we use any
OK, I'll add them to the next version.

> compiler tricks to create a build error when these are out of sync?
>When these states are out of range, they should enter "default" processing.

>> +		break;
>> +	default:
>> +		seq_printf(seq, "%s\n", "Invalid");
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +void vfio_device_debugfs_init(struct vfio_device *vdev)
>> +{
>> +	struct dentry *vfio_dev_migration = NULL;
>> +	struct device *dev = &vdev->device;
> 
> Nit, both of these could be defined within the scope of the mig_ops
> test below.
>

"vfio_dev_migration" can be placed under mig_ops, but "dev" is public.
Also, there should be no problem declaring variables like this.

>> +
>> +	vdev->debug_root = debugfs_create_dir(dev_name(vdev->dev), vfio_debugfs_root);
>> +
>> +	if (vdev->mig_ops) {
>> +		vfio_dev_migration = debugfs_create_dir("migration", vdev->debug_root);
>> +		debugfs_create_devm_seqfile(dev, "state", vfio_dev_migration,
>> +					  vfio_device_state_read);
>> +	}
>> +}
>> +
>> +void vfio_device_debugfs_exit(struct vfio_device *vdev)
>> +{
>> +	debugfs_remove_recursive(vdev->debug_root);
>> +}
>> +
>> +void vfio_debugfs_create_root(void)
>> +{
>> +	vfio_debugfs_root = debugfs_create_dir("vfio", NULL);
>> +}
>> +
>> +void vfio_debugfs_remove_root(void)
>> +{
>> +	debugfs_remove_recursive(vfio_debugfs_root);
>> +	vfio_debugfs_root = NULL;
>> +}
>> +
>> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
>> index cfad824d9aa2..8a7456f89842 100644
>> --- a/drivers/vfio/vfio_main.c
>> +++ b/drivers/vfio/vfio_main.c
>> @@ -309,7 +309,7 @@ static int __vfio_register_dev(struct vfio_device *device,
>>  
>>  	/* Refcounting can't start until the driver calls register */
>>  	refcount_set(&device->refcount, 1);
>> -
>> +	vfio_device_debugfs_init(device);
>>  	vfio_device_group_register(device);
>>  
>>  	return 0;
>> @@ -378,6 +378,7 @@ void vfio_unregister_group_dev(struct vfio_device *device)
>>  		}
>>  	}
>>  
>> +	vfio_device_debugfs_exit(device);
>>  	/* Balances vfio_device_set_group in register path */
>>  	vfio_device_remove_group(device);
>>  }
> 
> init/exit calls should try to be symmetric, if we call init before
> vfio_device_group_register() then we should call exit after
> vfio_device_group_unregister().  In this case, why shouldn't init be
> the last call in __vfio_register_dev() and exit the first call in
> vfio_unregister_group_dev()?
> 

OK, I would put vfio_device_debugfs_init() into vfio_device_group_register().

>> @@ -1662,6 +1663,7 @@ static int __init vfio_init(void)
>>  	if (ret)
>>  		goto err_alloc_dev_chrdev;
>>  
>> +	vfio_debugfs_create_root();
>>  	pr_info(DRIVER_DESC " version: " DRIVER_VERSION "\n");
>>  	return 0;
>>  
>> @@ -1684,6 +1686,7 @@ static void __exit vfio_cleanup(void)
>>  	vfio_virqfd_exit();
>>  	vfio_group_cleanup();
>>  	xa_destroy(&vfio_device_set_xa);
>> +	vfio_debugfs_remove_root();
>>  }
> 
> Same, if we create it last, let's remove it first.  The above creates
> it last and removes it last.  Thanks,
>

OK, I will adjust the order of vfio_debugfs_remove_root() in vfio_cleanup().

Thanks,
Longfang.

> Alex
> 
>>  
>>  module_init(vfio_init);
>> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
>> index 454e9295970c..769d7af86225 100644
>> --- a/include/linux/vfio.h
>> +++ b/include/linux/vfio.h
>> @@ -69,6 +69,13 @@ struct vfio_device {
>>  	u8 iommufd_attached:1;
>>  #endif
>>  	u8 cdev_opened:1;
>> +#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
>>  };
>>  
>>  /**
> 
> .
>