linux-kernel - Re: [RFC PATCH 00/20] Introduce the famfs shared-memory file system

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Date: Thu, 23 May 2024 19:47:08 -0500
From: John Groves <John@...ves.net>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: linux-cxl@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, nvdimm@...ts.linux.dev
Subject: Re: [RFC PATCH 00/20] Introduce the famfs shared-memory file system

On 24/05/23 03:57PM, Miklos Szeredi wrote:
> [trimming CC list]
> 
> On Thu, 23 May 2024 at 04:49, John Groves <John@...ves.net> wrote:
> 
> > - memmap=<size>!<hpa_offset> will reserve a pretend pmem device at <hpa_offset>
> > - memmap=<size>$<hpa_offset> will reserve a pretend dax device at <hpa_offset>
> 
> Doesn't get me a /dev/dax or /dev/pmem
> 
> Complete qemu command line:
> 
> qemu-kvm -s -serial none -parallel none -kernel
> /home/mszeredi/git/linux/arch/x86/boot/bzImage -drive
> format=raw,file=/home/mszeredi/root_fs,index=0,if=virtio -drive
> format=raw,file=/home/mszeredi/images/ubd1,index=1,if=virtio -chardev
> stdio,id=virtiocon0,signal=off -device virtio-serial -device
> virtconsole,chardev=virtiocon0 -cpu host -m 8G -net user -net
> nic,model=virtio -fsdev local,security_model=none,id=fsdev0,path=/home
> -device virtio-9p-pci,fsdev=fsdev0,mount_tag=hostshare -device
> virtio-rng-pci -smp 4 -append 'root=/dev/vda console=hvc0
> memmap=4G$4G'
> 
> root@kvm:~/famfs# scripts/chk_efi.sh
> This system is neither Ubuntu nor Fedora. It is identified as debian.
> /sys/firmware/efi not found; probably not efi
>  not found; probably nof efi
> /boot/efi/EFI not found; probably not efi
> /boot/efi/EFI/BOOT not found; probably not efi
> /boot/efi/EFI/ not found; probably not efi
> /boot/efi/EFI//grub.cfg not found; probably nof efi
> Probably not efi; errs=6
> 
> Thanks,
> Miklos


Apologies, but I'm short on time at the moment - going into a long holiday
weekend in the US with family plans. I should be focused again by middle of
next week.

But can you check /proc/cmdline to see of the memmap arg got through without
getting mangled? The '$' tends to get fubar'd. You might need \$, or I've seen
the need for \\\$. If it's un-mangled, there should be a dax device.

If that doesn't work, it's worth trying '!' instead, which I think would give
you a pmem device - if the arg gets through (but ! is less likely to get
horked). That pmem device can be converted to devdax...

Regards,
John