[stgt] RFC [patch] Search /sys/class/bsg/<ctl>/dev for bsg major number.

[Nicholas A. Bellinger]

On Sat, 2010-08-21 at 16:07 +1000, Mark Harvey wrote:
> Apologies for including this patch as an attachment..
> I haven't figured out how to successfully do it from the office.
> 
> Included inline for easier reading / review.
> 
> On Fri, Aug 20, 2010 at 7:29 PM, Nicholas A. Bellinger
> <nab at linux-iscsi.org> wrote:
> > On Fri, 2010-08-20 at 11:22 +0900, FUJITA Tomonori wrote:
> >> On Thu, 19 Aug 2010 12:51:54 -0700
> >> "Nicholas A. Bellinger" <nab at linux-iscsi.org> wrote:
> >> > So it looks like the failure is attributed to my hardcoding of major 254
> >> > in the original STGT/BSG patch (note the comment above the conditional
> >> > check).  Here is a quick fix:
> >> >
> >> > diff --git a/usr/bs_sg.c b/usr/bs_sg.c
> >> > index cda5cd2..a369570 100644
> >> > --- a/usr/bs_sg.c
> >> > +++ b/usr/bs_sg.c
> >> > @@ -289,7 +289,7 @@ static int chk_sg_device(char *path)
> >> >                 return 0;
> >> >
> >> >         /* This is not yet defined in include/linux/major.h.. */
> >> > -       if (major(st.st_rdev) == 254)
> >> > +       if ((major(st.st_rdev) == 254) || (major(st.st_rdev) == 253))
> >> >                 return 1;
> >> >
> >> >         return -1;
> >>
> >> Well, seems that nobody uses the bsg support except for you. :)
> >>
> >> The above patch is still wrong.
> >>
> >> bsg major number can be anything. So you need to get it from
> >> /proc/devices.
> >>
> >> Or you can also get it from /sys/class/bsg/, which is created by
> >> kernel so available on any distributions.
> >>
> >> You can steal the bsg device handling code from sg3-utils. Maybe
> >> someone could create something like libbsg.so
> >
> > Hmmm indeed, thanks for point this one out.   I will have look at
> > adressing for this the BSG efforts with STGT and QEMU-KVM using the
> > recommended major:minor output from /sys/class/bsg/$HCTL/dev.
> >
> > Best,
> >
> > --nab
> >
> >
> 
> >From a90611630879205ef497821552474e894d463c94 Mon Sep 17 00:00:00 2001
> From: Mark Harvey <markh794 at gmail.com>
> Date: Sat, 21 Aug 2010 15:22:48 +1000
> Subject: Check bsg major number from /sys/class/bsg/<c:t:l>/dev
> 
> Signed-off-by: Mark Harvey <markh794 at gmail.com>
> ---
>  usr/bs_sg.c |   35 ++++++++++++++++++++++++++++++++---
>  1 files changed, 32 insertions(+), 3 deletions(-)
> 
> diff --git a/usr/bs_sg.c b/usr/bs_sg.c
> index dfd49c3..7fc9787 100644
> --- a/usr/bs_sg.c
> +++ b/usr/bs_sg.c
> @@ -269,6 +269,34 @@ static void bs_sg_cmd_complete(int fd, int
> events, void *data)
>  	cmd->scsi_cmd_done(cmd, io_hdr.status);
>  }
> 
> +static int get_bsg_major(char *path)
> +{
> +	FILE *devfd;
> +	char majorno[8];
> +	char dev[128];
> +	int ch;
> +	int i;
> +
> +	dev[0] = '\0';
> +	strncat(dev, "/sys/class/bsg/", 16);
> +	strncat(dev, &path[9], 64);
> +	strncat(dev, "/dev", 5);
> +	devfd = fopen(dev, "r");
> +	if (!devfd)
> +		return -1;
> +	ch = fgetc(devfd);
> +	for (i = 0; i < 7; i++) {
> +		if (ch == ':') {
> +			majorno[i] = '\0';
> +			break;
> +		}
> +		majorno[i] = ch;
> +		ch = fgetc(devfd);
> +	}
> +	fclose(devfd);
> +	return atoi(majorno);
> +}
> +
>  static int chk_sg_device(char *path)
>  {
>  	struct stat st;
> @@ -287,9 +315,10 @@ static int chk_sg_device(char *path)
>  	if (major(st.st_rdev) == SCSI_GENERIC_MAJOR)
>  		return 0;
> 
> -	/* This is not yet defined in include/linux/major.h.. */
> -	if (major(st.st_rdev) == 254)
> -		return 1;
> +	if (!strncmp("/dev/bsg", path, 8)) {
> +		if (major(st.st_rdev) == get_bsg_major(path))
> +			return 0;
> +	}
> 
>  	return -1;
>  }

Hi Mark,

Here is my updated version of your initial code for the megasas
8708EM2 / SGL passthrough friendly qemu-kvm.git/scsi-bsg:

http://git.kernel.org/?p=virt/kvm/nab/qemu-kvm.git;a=commitdiff;h=075901d9bc1fea670bef84f55806f1bc8b2a5e9e

Please feel free to improve your patch using this code and respin
another patch for tomo-san to review.

Thanks!

--nab


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