Thomas Huth <th...@redhat.com> writes:
> On 03/04/2023 16.55, Markus Armbruster wrote:
>> Alex Bennée <alex.ben...@linaro.org> writes:
>>
>>> Markus Armbruster <arm...@redhat.com> writes:
>>>
>>>> Alex Bennée <alex.ben...@linaro.org> writes:
> ...
>>> I was under the impression things like -hda wouldn't work say on an Arm
>>> machine because you don't know what sort of interface you might be
>>> using and -hda implies IDE. Where is this macro substitution done?
>>
>> qemu_init() calls drive_add() for all these options.
>>
>> drive_add(TYPE, INDEX, FILE, OPTSTR) creates a QemuOpts in group
>> "drive". It sets "if" to if_name[TYPE] unless TYPE is IF_DEFAULT,
>> "index" to INDEX unless it's negative, and "file" to FILE unless it's
>> null. Then it parses OPTSTR on top.
>>
>> For -hdX, the call looks like
>>
>> drive_add(IF_DEFAULT, popt->index - QEMU_OPTION_hda, optarg,
>> HD_OPTS);
>>
>> We pass IF_DEFAULT, so "if" remains unset. "index" is set to 0 for
>> -hda, 1, for -hdb and so forth. "file" is set to the option argument.
>> Since HD_OPTS is "media=disk", we set "media" to "disk".
>>
>> The QemuOpts in config group "drive" get passed to drive_new() via
>> drive_init_func(). Unset "if" defaults to the current machine's class's
>> block_default_type.
>>
>> If a machine doesn't set this member explicitly, it remains zero, which
>> is IF_NONE. Documented in blockdev.h:
>>
>> typedef enum {
>> IF_DEFAULT = -1, /* for use with drive_add() only */
>> /*
>> * IF_NONE must be zero, because we want MachineClass member
>> ---> * block_default_type to default-initialize to IF_NONE
>> */
>> IF_NONE = 0,
>> IF_IDE, IF_SCSI, IF_FLOPPY, IF_PFLASH, IF_MTD, IF_SD, IF_VIRTIO,
>> IF_XEN,
>> IF_COUNT
>> } BlockInterfaceType;
>>
>> Questions?
>
> How's the average user supposed to know that? Our qemu-options.hx just says:
> "-hda/-hdb file use 'file' as IDE hard disk 0/1 image"...
Ancient doc bug. Should have been updated in commit 2d0d2837dcf
(Support default block interfaces per QEMUMachine) back in 2012.
