Problem with bootmem/mmap

[ZCane, Ed]

Dear all,

I'm allocating a large buffer at boot time (for later DMA purposes) using:

buf=alloc_bootmem_low_pages(1024*1024*500);

If I printk here, from init/main.c, I get:
buf=0xc1e14000
__va(buf)=0x81e14000
__pa(buf)=0x1e14000

Now, in user-space, I'm trying to get access to my buffer (as root), by
doing the following:

memfd=open("/dev/mem", O_RDWR);
my_buf=mmap(0, 1024*1024*501, PROT_READ|PROT_WRITE,
                        MAP_SHARED|MAP_FIXED, memfd, OFFSET);

I've tried all those addresses above, as the OFFSET, but it either generates
an illegal instruction,
or a segfault. Bit of a beginner, but learning fast, and I'd be _really_
greatful, if anyone could help me!

Many thanks,
Ed

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