On Monday, 2021-03-01 at 12:50:33 +01, Philippe Mathieu-Daudé wrote: > On 2/26/21 9:23 AM, David Edmondson wrote: >> On Friday, 2021-02-26 at 00:02:38 +01, Philippe Mathieu-Daudé wrote: >> >>> If the block drive is read-only we will model a "protected" flash >>> device. We can thus use memory_region_init_rom_device_from_file() >>> which mmap the backing file when creating the MemoryRegion. >>> If the same backing file is used by multiple QEMU instances, this >>> reduces the memory footprint (this is often the case with the >>> CODE flash image from OVMF and AAVMF). >>> >>> Suggested-by: Stefan Hajnoczi <stefa...@redhat.com> >>> Signed-off-by: Philippe Mathieu-Daudé <phi...@redhat.com> >>> --- >>> hw/block/pflash_cfi01.c | 20 ++++++++++++++------ >>> hw/block/pflash_cfi02.c | 18 ++++++++++++++---- >>> 2 files changed, 28 insertions(+), 10 deletions(-) >>> >>> diff --git a/hw/block/pflash_cfi01.c b/hw/block/pflash_cfi01.c >>> index a5fa8d8b74a..5757391df1c 100644 >>> --- a/hw/block/pflash_cfi01.c >>> +++ b/hw/block/pflash_cfi01.c >>> @@ -743,11 +743,19 @@ static void pflash_cfi01_realize(DeviceState *dev, >>> Error **errp) >>> pfl->ro = 0; >>> } >>> >>> - memory_region_init_rom_device( >>> - &pfl->mem, OBJECT(dev), >>> - &pflash_cfi01_ops, >>> - pfl, >>> - pfl->name, total_len, errp); >>> + if (pfl->blk && pfl->ro) { >>> + memory_region_init_rom_device_from_file(&pfl->mem, OBJECT(dev), >>> + &pflash_cfi01_ops, pfl, >>> + pfl->name, total_len, >>> + qemu_real_host_page_size, >>> + RAM_SHARED, >>> + blk_bs(pfl->blk)->filename, >> >> How will this behave if someone does: >> >> -drive file=OVMF_CODE.fd.qcow2,index=0,if=pflash,format=qcow2,readonly=on >> >> Honestly, I'm not sure why they would, but it works today. > > OK I can add a check for "raw" driver, but I don't know to check for > offset == 0.
This is pretty much where I got to when I tried using mmap() and gave up (mostly because I figured that adding layer violating checks to the pflash driver would not be well received, but also because we don't share the same underlying file between multiple VMs and I wasn't sure that it would eventually work well for writable devices). dme. -- Driving at 90 down those country lanes, singing to "Tiny Dancer".