linux-kernel - Re: [PATCH 5/6] tools: hv: Add new fcopy application based on uio driver

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Message-ID: <20240219102354.GA12268@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date: Mon, 19 Feb 2024 02:23:54 -0800
From: Saurabh Singh Sengar <ssengar@...ux.microsoft.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
	decui@...rosoft.com, linux-hyperv@...r.kernel.org,
	linux-kernel@...r.kernel.org, ssengar@...rosoft.com
Subject: Re: [PATCH 5/6] tools: hv: Add new fcopy application based on uio
 driver

On Mon, Feb 19, 2024 at 10:52:12AM +0100, Greg KH wrote:
> On Mon, Feb 19, 2024 at 01:24:21AM -0800, Saurabh Singh Sengar wrote:
> > > > +#define HV_RING_SIZE		(4 * 4096)
> > > 
> > > Hey, that doesn't match the kernel driver!  Why these values?
> > 
> > This application talks to device which is recognize as HV_FCOPY
> > is kernel. In the first patch of current patch series I have
> > mentioned .pref_ring_size = 0x4000 for HV_FCOPY which matches this.
> > 
> > This code is well tested.
> 
> I'm commenting on the fact the 4096 is sometimes PAGE_SIZE and sometimes
> not, and you have a default of using PAGE_SIZE values in the kernel
> driver, and as such, this will not match up.  So be careful here.

Thanks for clarification, I will add some note for it in V2.

> 
> > > > +
> > > > +unsigned char desc[HV_RING_SIZE];
> > > > +
> > > > +static int target_fd;
> > > > +static char target_fname[PATH_MAX];
> > > > +static unsigned long long filesize;
> > > > +
> > > > +static int hv_fcopy_create_file(char *file_name, char *path_name, __u32 flags)
> > > > +{
> > > > +	int error = HV_E_FAIL;
> > > > +	char *q, *p;
> > > > +
> > > > +	filesize = 0;
> > > > +	p = (char *)path_name;
> > > 
> > > Why the unneeded cast?
> > 
> > This code is existing today as form of hv_fcopy_daemon. As this new
> > application is replacing hv_fcopy_daemon I reused the same code and
> > casting.
> 
> That wasn't obvious that this was copied code, please be explicit about
> that.
> 
> thanks,
> 
> greg k-h