Re: [PATCH v7 1/5] vfio/migration: Add debugfs to live migration driver

From: liulongfang
Date: Tue Jan 31 2023 - 22:20:17 EST

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In reply to: Alex Williamson: "Re: [PATCH v7 1/5] vfio/migration: Add debugfs to live migration driver"
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On 2023/1/27 3:27, Alex Williamson wrote:
> On Fri, 20 Jan 2023 11:29:26 +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 |
>> | |
>> | |
>> +-----+-------------------------+----------+
>> | ^ | ^
>> v | v |
>> +-----+--+ +-----+--+
>> | src VF | | dst VF |
>> +-+------+ +-+------+
>> | ^ | ^
>> v | v |
>> +-------+-+------+ +-------+-+------+
>> |Debugfs|state | |Debugfs|state |
>> +-------+--------+ +-------+--------+
>> | debug_root | | debug_root |
>> +-------+--------+ +-------+--------+
>>
>> 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_pci_debugfs.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_mig" file.
>> then create a "debug_root" file for each live migration VF device.
>
> s/VF // In practice it may be VFs, but I don't think we want to
> artificially imply that the device must be a VF. In fact, I'm not sure

Yes, the description should be modified here, and it should not be limited
to only support VF.

> why any of this code lives in vfio/pci/ vs vfio/, there's nothing PCI
> specific here. Why isn't all of this done in vfio_main to be shared
> with both pci and non-pci vfio drivers and devices?
>

Combined with your observations below, I think it is more appropriate to
create a "vfio-pci" directory here, because the current live migration
function is still used on pci devices.

For non-pci devices, if there is a device that needs to add debugfs,
then it can create a similar directory.

>> state file: used to get the status of the live migration device.
>> debug_root: used to create your own custom debug files for live
>> migration device drivers.
>>
>> 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/pci/Makefile | 1 +
>> drivers/vfio/pci/vfio_pci_core.c | 3 ++
>> drivers/vfio/pci/vfio_pci_debugfs.c | 80 +++++++++++++++++++++++++++++
>> drivers/vfio/pci/vfio_pci_debugfs.h | 28 ++++++++++
>> include/linux/vfio.h | 8 +++
>> 5 files changed, 120 insertions(+)
>> create mode 100644 drivers/vfio/pci/vfio_pci_debugfs.c
>> create mode 100644 drivers/vfio/pci/vfio_pci_debugfs.h
>>
>> diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
>> index 24c524224da5..75fe37e72e8d 100644
>> --- a/drivers/vfio/pci/Makefile
>> +++ b/drivers/vfio/pci/Makefile
>> @@ -2,6 +2,7 @@
>>
>> vfio-pci-core-y := vfio_pci_core.o vfio_pci_intrs.o vfio_pci_rdwr.o vfio_pci_config.o
>> vfio-pci-core-$(CONFIG_VFIO_PCI_ZDEV_KVM) += vfio_pci_zdev.o
>> +vfio-pci-core-$(CONFIG_DEBUG_FS) += vfio_pci_debugfs.o
>> obj-$(CONFIG_VFIO_PCI_CORE) += vfio-pci-core.o
>>
>> vfio-pci-y := vfio_pci.o
>> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
>> index f9365a5bc961..e85df2deb8e6 100644
>> --- a/drivers/vfio/pci/vfio_pci_core.c
>> +++ b/drivers/vfio/pci/vfio_pci_core.c
>> @@ -31,6 +31,7 @@
>> #include <asm/eeh.h>
>> #endif
>>
>> +#include "vfio_pci_debugfs.h"
>> #include "vfio_pci_priv.h"
>>
>> #define DRIVER_AUTHOR "Alex Williamson <alex.williamson@xxxxxxxxxx>"
>> @@ -2555,11 +2556,13 @@ EXPORT_SYMBOL_GPL(vfio_pci_core_set_params);
>>
>> static void vfio_pci_core_cleanup(void)
>> {
>> + vfio_pci_debugfs_remove_root();
>> vfio_pci_uninit_perm_bits();
>> }
>>
>> static int __init vfio_pci_core_init(void)
>> {
>> + vfio_pci_debugfs_create_root();
>> /* Allocate shared config space permission data used by all devices */
>> return vfio_pci_init_perm_bits();
>> }
>> diff --git a/drivers/vfio/pci/vfio_pci_debugfs.c b/drivers/vfio/pci/vfio_pci_debugfs.c
>> new file mode 100644
>> index 000000000000..0bcf0bf034e5
>> --- /dev/null
>> +++ b/drivers/vfio/pci/vfio_pci_debugfs.c
>> @@ -0,0 +1,80 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * Copyright (c) 2023, HiSilicon Ltd.
>> + */
>> +
>> +#include <linux/pci.h>
>> +#include <linux/vfio_pci_core.h>
>> +
>> +#include "vfio_pci_debugfs.h"
>> +
>> +static struct dentry *vfio_pci_debugfs_root;
>> +
>> +static int vfio_pci_vf_state_read(struct seq_file *seq, void *data)
>> +{
>> + struct device *vf_dev = seq->private;
>> + struct vfio_pci_core_device *core_device = dev_get_drvdata(vf_dev);
>> + struct vfio_device *vdev = &core_device->vdev;
>> + 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", "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_pci_vf_debugfs_init(struct vfio_device *vdev)
>> +{
>> + struct device *dev = vdev->dev;
>> +
>> + vdev->debug_root = debugfs_create_dir(dev_name(dev), vfio_pci_debugfs_root);
>> +
>> + debugfs_create_devm_seqfile(dev, "state", vdev->debug_root,
>> + vfio_pci_vf_state_read);
>> +}
>> +EXPORT_SYMBOL_GPL(vfio_pci_vf_debugfs_init);
>> +
>> +void vfio_pci_vf_debugfs_exit(struct vfio_device *vdev)
>> +{
>> + debugfs_remove_recursive(vdev->debug_root);
>> +}
>> +EXPORT_SYMBOL_GPL(vfio_pci_vf_debugfs_exit);
>> +
>> +void vfio_pci_debugfs_create_root(void)
>> +{
>> + vfio_pci_debugfs_root = debugfs_create_dir("vfio_mig", NULL);
>
> Is this hierarchical, ie. should we have "vfio/migration/" such that we
> can introduce other debugfs entries w/o creating vfio_foo, vfio_bar,
> vfio_baz, etc. Otherwise the core or pci-core should only initialize a
> "vfio" or "vfio-pci" root and the above init and exit interfaces should
> be migration specific, creating "migrations_state" and only removing
> the entries on exit that their companion init function created.
>

Yes, your suggestion is very good. Here I also agree to create a "vfio-pci"
directory.In addition, it is not easy to create a "migration" subdirectory
internally,because there is no valid basis for judging whether to create a
"migration" directory when creating a vfio-pci directory.
Therefore, it is simpler to create migration_state directly with migration
as a prefix.

>> +}
>> +EXPORT_SYMBOL_GPL(vfio_pci_debugfs_create_root);
>> +
>> +void vfio_pci_debugfs_remove_root(void)
>> +{
>> + debugfs_remove_recursive(vfio_pci_debugfs_root);
>> + vfio_pci_debugfs_root = NULL;
>> +}
>> +EXPORT_SYMBOL_GPL(vfio_pci_debugfs_remove_root);
>> +
>> diff --git a/drivers/vfio/pci/vfio_pci_debugfs.h b/drivers/vfio/pci/vfio_pci_debugfs.h
>> new file mode 100644
>> index 000000000000..beaaa709725e
>> --- /dev/null
>> +++ b/drivers/vfio/pci/vfio_pci_debugfs.h
>> @@ -0,0 +1,28 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/*
>> + * vfio_pci_debugfs.h - VFIO migration debugfs interface
>> + *
>> + * Copyright (c) 2023, HiSilicon Ltd.
>> + *
>> + * Author: Longfang Liu <liulongfang@xxxxxxxxxx>
>> + */
>> +
>> +#ifndef __VFIO_PCI_DEBUGFS_H
>> +#define __VFIO_PCI_DEBUGFS_H
>> +
>> +#include <linux/debugfs.h>
>> +#include <linux/vfio.h>
>> +
>> +#ifdef CONFIG_DEBUG_FS
>> +void vfio_pci_debugfs_create_root(void);
>> +void vfio_pci_debugfs_remove_root(void);
>> +void vfio_pci_vf_debugfs_init(struct vfio_device *vdev);
>> +void vfio_pci_vf_debugfs_exit(struct vfio_device *vdev);
>> +#else
>> +static inline void vfio_pci_debugfs_create_root(void) {}
>> +static inline void vfio_pci_debugfs_remove_root(void) {}
>> +static inline void vfio_pci_vf_debugfs_init(struct vfio_device *vdev) {}
>> +static inline void vfio_pci_vf_debugfs_exit(struct vfio_device *vdev) {}
>> +#endif /* CONFIG_DEBUG_FS */
>> +
>> +#endif /* __VFIO_PCI_DEBUGFS_H */
>
> With the above changes, declarations should probably just exist in
> drivers/vfio/vfio.h. Thanks,
>

Ok, then I'll delete this header file and put them directly in vfio.h

> Alex
>
Thanks,
Longfang.

>> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
>> index b4d5d4ca3d7d..b4bc8dfe8413 100644
>> --- a/include/linux/vfio.h
>> +++ b/include/linux/vfio.h
>> @@ -54,6 +54,14 @@ struct vfio_device {
>> struct completion comp;
>> struct list_head group_next;
>> struct list_head iommu_entry;
>> +
>> +#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
>> };
>>
>> /**
>
> .
>

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Previous message: Stephen Rothwell: "linux-next: duplicate patch in the icc tree"
In reply to: Alex Williamson: "Re: [PATCH v7 1/5] vfio/migration: Add debugfs to live migration driver"
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