Subject: Re: [PATCH rdma-next 1/5] RDMA/core: Provide getter and setter to access IB device name

From: Jason Gunthorpe <[email-masked]>
Date: Thu, 20 Sep 2018 09:15:41 -0600

On Thu, Sep 20, 2018 at 02:21:58PM +0300, Leon Romanovsky wrote:
> From: Leon Romanovsky <[email-masked]>
> 
> Prepare IB device name field to rename operation by ensuring that all
> accesses to it are protected with lock and users don't see part of name.

Oh dear, no, that isn't going to work, there is too much stuff using
dev_name.. Did you read the comment on device_rename??

https://elixir.bootlin.com/linux/v4.19-rc4/source/drivers/base/core.c#L2715

> The protection is done with global device_lock because it is used in
> allocation and deallocation phases. At this stage, this lock is not
> busy and easily can be moved to be per-device, once it will be needed.
> 
> Signed-off-by: Leon Romanovsky <[email-masked]>
>  drivers/infiniband/core/device.c | 24 +++++++++++++++++++++++-
>  include/rdma/ib_verbs.h          |  8 +++++++-
>  2 files changed, 30 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/infiniband/core/device.c b/drivers/infiniband/core/device.c
> index 5a680a88aa87..3270cde6d806 100644
> +++ b/drivers/infiniband/core/device.c
> @@ -170,6 +170,14 @@ static struct ib_device *__ib_device_get_by_name(const char *name)
>  	return NULL;
>  }
> 
> +void ib_device_get_name(struct ib_device *ibdev, char *name)
> +{
> +	down_read(&lists_rwsem);
> +	strlcpy(name, ibdev->name, IB_DEVICE_NAME_MAX);
> +	up_read(&lists_rwsem);
> +}
> +EXPORT_SYMBOL(ib_device_get_name);

I think we have to follow netdev and just rely on device_rename()
being 'good enough'.  

Switch everything to use dev_name()/etc rather than try and do
something like this so the responsibility is on the device core to
keep this working, not us.

Turns out I have a series for that for unrelated reasons..

>  static int alloc_name(char *name)
>  {
>  	unsigned long *inuse;
> @@ -202,6 +210,21 @@ static int alloc_name(char *name)
>  	return 0;
>  }
> 
> +int ib_device_alloc_name(struct ib_device *ibdev, const char *pattern)
> +{
> +	int ret = 0;
> +
> +	mutex_lock(&device_mutex);
> +	strlcpy(ibdev->name, pattern, IB_DEVICE_NAME_MAX);
> +	if (strchr(ibdev->name, '%'))
> +		ret = alloc_name(ibdev->name);
> +
> +	mutex_unlock(&device_mutex);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(ib_device_alloc_name);

Can't call alloc_name() without also adding to the list, this will
allow duplicates.

Jason