On Wed, 04 Sep 2019 at 19:54:51 +0200, Guilhem Moulin wrote: > $ qemu-system-x86_64 -display none \ > -add-fd "fd=3,set=0" \ > -drive "file=/dev/fdset/0,format=raw,media=disk" \ > 3<>/tmp/disk.img > qemu-system-x86_64: -drive file=/dev/fdset/0,format=raw,media=disk: Could > not open '/dev/fdset/0': Permission denied
Unsurprisingly it doesn't work if the file descriptor is read-only
$ qemu-system-x86_64 -display none \
-add-fd "fd=3,set=0" \
-drive "file=/dev/fdset/0,format=raw,media=disk" \
3</tmp/disk.img
qemu-system-x86_64: Initialization of device ide-hd failed: Could not
reopen file: Permission denied
but weirdly enough it does work when *another* read-only FD is added to
the FD set containing the read-write descriptor:
$ qemu-system-x86_64 -display none \
-add-fd "fd=3,set=0" -add-fd "fd=4,set=0" \
-drive "file=/dev/fdset/0,format=raw,media=disk" \
3<>/tmp/disk.img 4</tmp/disk.img
Reading again the documentation, it's not entirely clear to me that that
a single (read-write) descriptor per FD is in fact enough for a block
node, but I have hard time believing that wasting a descriptor per image
is intentional.
--
Guilhem.
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