Re: [Qemu-devel] [PATCH v5 4/4] i386: allow to load initrd below 4G for recent linux

[Li Zhijian]

Hi Eduardo


On 1/15/19 01:53, Eduardo Habkost wrote:
> > +    if (protocol >= 0x20c &&
> > +        lduw_p(header+0x236) & XLF_CAN_BE_LOADED_ABOVE_4G) {
> > +        /*
> > +         * Linux has supported initrd up to 4 GB for a very long time (2007,
> > +         * long before XLF_CAN_BE_LOADED_ABOVE_4G which was added in 2013),
> > +         * though it only sets initrd_max to 2 GB to "work around bootloader
> > +         * bugs". Luckily, QEMU firmware(which does something like bootloader)
> > +         * has supported this.
> > +         *
> > +         * It's believed that if XLF_CAN_BE_LOADED_ABOVE_4G is set, initrd can
> > +         * be loaded into any address.
> > +         *
> > +         * In addition, initrd_max is uint32_t simply because QEMU doesn't
> > +         * support the 64-bit boot protocol (specifically the ext_ramdisk_image
> > +         * field).
> > +         *
> > +         * Therefore here just limit initrd_max to UINT32_MAX simply as well.
> > +         *
> > +         * FIXME: it's possible that linux protocol within [0x208, 0x20c]
> > +         * supports up to 4G initrd as well.
> I don't understand what exactly this FIXME comment is
> documenting.  What exactly needs to be fixed?
XLF_CAN_BE_LOADED_ABOVE_4G is one of the indicators, actually as comments said,
linux has supported up to 4 GB initrd since linux-2.26(protocol version 0x208).


I just want to comment that linux with protocol within [0x208, 0x20c] supports 
up to 4 GB initrd as well.

Is documenting with FIXME appropriate?


Thanks