Re: [PATCH v17 1/2] vfio/migration: Add debugfs to live migration driver

[liulongfang]

On 2023/10/16 23:17, Cédric Le Goater wrote:
> Hello Longfang,
> 
> On 10/13/23 11:04, Longfang Liu 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                     |
>>      |                                           |
>>      |                                           |
>>      +---+----------------------------+----------+
>>          |      ^                     |      ^
>>          |      |                     |      |
>>          |      |                     |      |
>>          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".
>>
>> Signed-off-by: Longfang Liu <liulongfang@xxxxxxxxxx>
>> ---
>>   drivers/vfio/Kconfig      | 10 +++++
>>   drivers/vfio/Makefile     |  1 +
>>   drivers/vfio/debugfs.c    | 90 +++++++++++++++++++++++++++++++++++++++
>>   drivers/vfio/vfio.h       | 14 ++++++
>>   drivers/vfio/vfio_main.c  | 14 +++++-
>>   include/linux/vfio.h      |  7 +++
>>   include/uapi/linux/vfio.h |  1 +
>>   7 files changed, 135 insertions(+), 2 deletions(-)
>>   create mode 100644 drivers/vfio/debugfs.c
>>
>> diff --git a/drivers/vfio/Kconfig b/drivers/vfio/Kconfig
>> index 6bda6dbb4878..ceae52fd7586 100644
>> --- a/drivers/vfio/Kconfig
>> +++ b/drivers/vfio/Kconfig
>> @@ -80,6 +80,16 @@ config VFIO_VIRQFD
>>       select EVENTFD
>>       default n
>>   +config VFIO_DEBUGFS
>> +    bool "Export VFIO internals in DebugFS"
>> +    depends on DEBUG_FS
>> +    help
>> +      Allows exposure of VFIO device internals. This option enables
>> +      the use of debugfs by VFIO drivers as required. The device can
>> +      cause the VFIO code create a top-level debug/vfio directory
>> +      during initialization, and then populate a subdirectory with
>> +      entries as required.
>> +
>>   source "drivers/vfio/pci/Kconfig"
>>   source "drivers/vfio/platform/Kconfig"
>>   source "drivers/vfio/mdev/Kconfig"
>> diff --git a/drivers/vfio/Makefile b/drivers/vfio/Makefile
>> index c82ea032d352..d43a699d55b1 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-$(CONFIG_VFIO_DEBUGFS) += debugfs.o
>>     obj-$(CONFIG_VFIO_IOMMU_TYPE1) += vfio_iommu_type1.o
>>   obj-$(CONFIG_VFIO_IOMMU_SPAPR_TCE) += vfio_iommu_spapr_tce.o
>> diff --git a/drivers/vfio/debugfs.c b/drivers/vfio/debugfs.c
>> new file mode 100644
>> index 000000000000..ae53d6110f47
>> --- /dev/null
>> +++ b/drivers/vfio/debugfs.c
>> @@ -0,0 +1,90 @@
>> +// 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;
>> +
>> +    BUILD_BUG_ON(VFIO_DEVICE_STATE_NR !=
>> +        VFIO_DEVICE_STATE_PRE_COPY_P2P + 1);
>> +
>> +    ret = vdev->mig_ops->migration_get_state(vdev, &state);
>> +    if (ret)
>> +        return -EINVAL;
>> +
>> +    switch (state) {
>> +    case VFIO_DEVICE_STATE_ERROR:
>> +        seq_printf(seq, "%s\n", "ERROR");
>> +        break;
>> +    case VFIO_DEVICE_STATE_STOP:
>> +        seq_printf(seq, "%s\n", "STOP");
>> +        break;
>> +    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_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_PRE_COPY:
>> +        seq_printf(seq, "%s\n", "PRE_COPY");
>> +        break;
>> +    case VFIO_DEVICE_STATE_PRE_COPY_P2P:
>> +        seq_printf(seq, "%s\n", "PRE_COPY_P2P");
>> +        break;
>> +    default:
>> +        seq_printf(seq, "%s\n", "Invalid");
> 
> seq_puts() is more appropriate than seq_printf() above.
>

There is no difference between seq_puts() and seq_printf() here,
no need to modify it.

> I would suggest to add an array or some helper, that the VFIO drivers
> could use to debug the migration flow with pr_* primitives. It can be
> done later.
>

If you want to debug this migration process in the VFIO driver,
you can refer to vdev->mig_ops->migration_get_state() to read the status.

> 
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>> +void vfio_device_debugfs_init(struct vfio_device *vdev)
>> +{
>> +    struct device *dev = &vdev->device;
>> +
>> +    vdev->debug_root = debugfs_create_dir(dev_name(vdev->dev), vfio_debugfs_root);
>> +
>> +    if (vdev->mig_ops) {
>> +        struct dentry *vfio_dev_migration = NULL;
> 
> mig_dir maybe ?
>

"vfio_dev_migration " will not affect the readability of the code.

> It would be easier to understand the nature of the variable IMHO.
> 
>> +
>> +        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.h b/drivers/vfio/vfio.h
>> index 307e3f29b527..bde84ad344e5 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_VFIO_DEBUGFS
>> +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_VFIO_DEBUGFS */
>> +
>>   #endif
>> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
>> index e31e1952d7b8..9aec4c22f051 100644
>> --- a/drivers/vfio/vfio_main.c
>> +++ b/drivers/vfio/vfio_main.c
>> @@ -309,7 +309,6 @@ static int __vfio_register_dev(struct vfio_device *device,
>>         /* Refcounting can't start until the driver calls register */
>>       refcount_set(&device->refcount, 1);
>> -
> 
> superfluous change.
>

A blank line here is to separate it from the comment above.
Makes it easier to be read.

>>       vfio_device_group_register(device);
>>         return 0;
>> @@ -320,7 +319,15 @@ static int __vfio_register_dev(struct vfio_device *device,
>>     int vfio_register_group_dev(struct vfio_device *device)
>>   {
>> -    return __vfio_register_dev(device, VFIO_IOMMU);
>> +    int ret;
>> +
>> +    ret = __vfio_register_dev(device, VFIO_IOMMU);
>> +    if (ret)
>> +        return ret;
>> +
>> +    vfio_device_debugfs_init(device);
> 
> Can it be called from __vfio_register_dev() instead ? and mdev devices
> would get debugfs support also.
>

This is for symmetry in function calls.
The need for symmetry was mentioned in the previous review.

> Thanks,
> 
> C.
>
Thanks,
Longfang.

>> +
>> +    return 0;
>>   }
>>   EXPORT_SYMBOL_GPL(vfio_register_group_dev);
>>   @@ -378,6 +385,7 @@ 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);
>>   }
>> @@ -1676,6 +1684,7 @@ 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;
>>   @@ -1691,6 +1700,7 @@ static int __init vfio_init(void)
>>     static void __exit vfio_cleanup(void)
>>   {
>> +    vfio_debugfs_remove_root();
>>       ida_destroy(&vfio.device_ida);
>>       vfio_cdev_cleanup();
>>       class_destroy(vfio.device_class);
>> 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
>>   };
>>     /**
>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
>> index 7f5fb010226d..2b68e6cdf190 100644
>> --- a/include/uapi/linux/vfio.h
>> +++ b/include/uapi/linux/vfio.h
>> @@ -1219,6 +1219,7 @@ enum vfio_device_mig_state {
>>       VFIO_DEVICE_STATE_RUNNING_P2P = 5,
>>       VFIO_DEVICE_STATE_PRE_COPY = 6,
>>       VFIO_DEVICE_STATE_PRE_COPY_P2P = 7,
>> +    VFIO_DEVICE_STATE_NR,
>>   };
>>     /**
> 
> .
>