Hi,
I am using debian 10 container to compile qemu too. I think that what happens here is that /usr/include/linux/swab.h Uses BITS_PER_LONG instead of __BITS_PER_LONG which is actually defined before in qemu at: include/qemu/bitops.h:#define BITS_PER_LONG (sizeof (unsigned long) * BITS_PER_BYTE) which injects this definition into the linux swab.h header. By changing BITS_PER_LONG to __BITS_PER_LONG in the linux headers, I managed to successfully compile qemu. A different approach would be to move the linux header includes (#include <linux/cdrom.h>) in file-posix.c above all other includes - which in some way makes more sense (since we probaly don't want qemu defines to control linux headers) but it requires a more complex refactoring.
