On 04/12/19 09:52, Markus Armbruster wrote:
> Laszlo Ersek <ler...@redhat.com> writes:
>
>> On 04/11/19 21:50, Laszlo Ersek wrote:
>>> On 04/11/19 21:35, Laszlo Ersek wrote:
>>>> On 04/11/19 15:56, Markus Armbruster wrote:
>>>>> Factored out of pc_system_firmware_init() so the next commit can reuse
>>>>> it in hw/arm/virt.c.
>>>>>
>>>>> Signed-off-by: Markus Armbruster <arm...@redhat.com>
>>>>> ---
>>>>> hw/block/pflash_cfi01.c | 30 ++++++++++++++++++++++++++++++
>>>>> hw/i386/pc_sysfw.c | 19 ++-----------------
>>>>> include/hw/block/flash.h | 1 +
>>>>> 3 files changed, 33 insertions(+), 17 deletions(-)
>>>>>
>>>>> diff --git a/hw/block/pflash_cfi01.c b/hw/block/pflash_cfi01.c
>>>>> index 16dfae14b8..eba01b1447 100644
>>>>> --- a/hw/block/pflash_cfi01.c
>>>>> +++ b/hw/block/pflash_cfi01.c
>>>>> @@ -44,9 +44,12 @@
>>>>> #include "qapi/error.h"
>>>>> #include "qemu/timer.h"
>>>>> #include "qemu/bitops.h"
>>>>> +#include "qemu/error-report.h"
>>>>> #include "qemu/host-utils.h"
>>>>> #include "qemu/log.h"
>>>>> +#include "qemu/option.h"
>>>>> #include "hw/sysbus.h"
>>>>> +#include "sysemu/blockdev.h"
>>>>> #include "sysemu/sysemu.h"
>>>>> #include "trace.h"
>>>>>
>>>>> @@ -968,6 +971,33 @@ MemoryRegion *pflash_cfi01_get_memory(PFlashCFI01
>>>>> *fl)
>>>>> return &fl->mem;
>>>>> }
>>>>>
>>>>> +/*
>>>>> + * Handle -drive if=pflash for machines that use machine properties.
>>>>
>>>> (1) Can we improve readability with quotes? "-drive if=pflash"
>
> Sure.
>
>>>>> + * Map unit#i (0 < i <= @ndev) to @dev[i]'s property "drive".
>>>>
>>>> (2) I think you meant (0 <= i < @ndev)
>
> You're right, of course.
>
>>>>> + */
>>>>> +void pflash_cfi01_legacy_drive(PFlashCFI01 *dev[], int ndev)
>>>>> +{
>>>>> + int i;
>>>>
>>>> (3) For utter pedantry, "ndev" and "i" should have type "size_t" (in
>>>> particular because we expect the caller to fill "ndev" with ARRAY_SIZE().
>>>>
>>>> But, this would go beyond refactoring -- the original "int"s have served
>>>> us just fine, and we're usually counting up (exclusively) to the huge
>>>> number... two. :)
>
> Exactly!
>
>>>>> + DriveInfo *dinfo;
>>>>> + Location loc;
>>>>> +
>>>>> + for (i = 0; i < ndev; i++) {
>>>>> + dinfo = drive_get(IF_PFLASH, 0, i);
>>>>> + if (!dinfo) {
>>>>> + continue;
>>>>> + }
>>>>> + loc_push_none(&loc);
>>>>> + qemu_opts_loc_restore(dinfo->opts);
>>>>> + if (dev[i]->blk) {
>>>>
>>>> (4) Is this really identical to the code being removed? The above
>>>> controlling expression amounts to:
>>>>
>>>> pcms->flash[i]->blk
>>>>
>>>> but the original boils down to
>>>>
>>>> pflash_cfi01_get_blk(pcms->flash[i])
>>>>
>>>> Hmm... looking at pflash_cfi01_get_blk(), they are the same. Is there a
>>>> particular reason for not using the wrapper function any longer? As in:
>>>>
>>>> pflash_cfi01_get_blk(dev[i])
>
> I don't see the benefit in abstracting from the member access.
>
> If I could have ->blk outside pflash_cfi01.c without having to expose
> all of PFlashCFI01, and have it read-only, I would. But this is C, so I
> get to write yet another accessor function.
>
>>>>> + error_report("clashes with -machine");
>>>>> + exit(1);
>>>>> + }
>>>>> + qdev_prop_set_drive(DEVICE(dev[i]), "drive",
>>>>> + blk_by_legacy_dinfo(dinfo), &error_fatal);
>>>>> + loc_pop(&loc);
>>>>> + }
>>>>> +}
>>>>> +
>>>>> static void postload_update_cb(void *opaque, int running, RunState state)
>>>>> {
>>>>> PFlashCFI01 *pfl = opaque;
>>>>> diff --git a/hw/i386/pc_sysfw.c b/hw/i386/pc_sysfw.c
>>>>> index c628540774..d58e47184c 100644
>>>>> --- a/hw/i386/pc_sysfw.c
>>>>> +++ b/hw/i386/pc_sysfw.c
>>>>> @@ -269,32 +269,17 @@ void pc_system_firmware_init(PCMachineState *pcms,
>>>>> {
>>>>> PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
>>>>> int i;
>>>>> - DriveInfo *pflash_drv;
>>>>> BlockBackend *pflash_blk[ARRAY_SIZE(pcms->flash)];
>>>>> - Location loc;
>>>>>
>>>>> if (!pcmc->pci_enabled) {
>>>>> old_pc_system_rom_init(rom_memory, true);
>>>>> return;
>>>>> }
>>>>>
>>>>> - /* Map legacy -drive if=pflash to machine properties */
>>>>> + pflash_cfi01_legacy_drive(pcms->flash, ARRAY_SIZE(pcms->flash));
>>>>> +
>>>>> for (i = 0; i < ARRAY_SIZE(pcms->flash); i++) {
>>>>> pflash_blk[i] = pflash_cfi01_get_blk(pcms->flash[i]);
>>>>> - pflash_drv = drive_get(IF_PFLASH, 0, i);
>>>>> - if (!pflash_drv) {
>>>>> - continue;
>>>>> - }
>>>>> - loc_push_none(&loc);
>>>>> - qemu_opts_loc_restore(pflash_drv->opts);
>>>>> - if (pflash_blk[i]) {
>>>>> - error_report("clashes with -machine");
>>>>> - exit(1);
>>>>> - }
>>>>> - pflash_blk[i] = blk_by_legacy_dinfo(pflash_drv);
>>>>> - qdev_prop_set_drive(DEVICE(pcms->flash[i]),
>>>>> - "drive", pflash_blk[i], &error_fatal);
>>>>> - loc_pop(&loc);
>>>>> }
>>>>
>>>> (5) I think you deleted too much here. After this loop, post-patch, for
>>>> all "i", we'll have
>>>>
>>>> pflash_blk[i] = pflash_cfi01_get_blk(pcms->flash[i]);
>>>>
>>>> But pre-patch, for all "i" where the "continue" didn't fire, we'd end up
>>>> with:
>>>>
>>>> pflash_blk[i] = blk_by_legacy_dinfo(pflash_drv);
>>>>
>>>> IOW the original loop both verifies and *collects*, for the gap check
>>>> that comes just below.
>>>>
>>>> IIRC, this allows for mixing "-drive if=pflash,unit=N" with the machine
>>>> properties, as long as you have neither conflicts, nor gaps.
>>>>
>>>> Post-patch however, this kind of mixing would break, because we'd report
>>>> gaps for the legacy ("-drive if=pflash") options.
>>>>
>>>>
>>>> In addition, it could break the "use ROM mode" branch below, which is
>>>> based on pflash_blk[0].
>>>>
>>>> I think we should extend pflash_cfi01_legacy_drive() to populate
>>>> "pflash_blk[0..(ndev-1)]" on output (assuming pflash_blk is not NULL on
>>>> input).
>>>>
>>>> (Because, I'm assuming that qdev_prop_set_drive() -- which now occurs in
>>>> the factored-out loop *before* the loop that we preserve here -- has no
>>>> effect on pflash_cfi01_get_blk(pcms->flash[i]).)
>>>
>>> Hmmm, that's likely precisely what I'm wrong about. I've now looked at
>>> DEFINE_PROP_DRIVE / qdev_prop_drive / set_drive / parse_drive... Does
>>> qdev_prop_set_drive() actually *turn* the legacy options into genuine
>>> machine type properties?... The removed comment does indicate that:
>>>
>>> "Map legacy -drive if=pflash to machine properties"
>>>
>>> So I guess the remaining loop is correct after all, but the new comment
>>>
>>> "Handle -drive if=pflash for machines that use machine properties"
>>>
>>> is less clear to me.
>
> In my defense, the complete new comment is
>
> /*
> * Handle -drive if=pflash for machines that use machine properties.
> * Map unit#i (0 < i <= @ndev) to @dev[i]'s property "drive".
> */
>
>> OK, OK. I'm being dense. I guess the case is that
>>
>> qdev_prop_set_drive(DEVICE(dev[i]), "drive",
>> blk_by_legacy_dinfo(dinfo), &error_fatal);
>>
>> in the new function basically *assigns* a non-NULL value to
>>
>> dev[i]->blk
>>
>> which was checked to be NULL just before.
>
> Correct!
>
> Aside: the workings of qdev_prop_set_drive() used to be reasonably
> obvious until we rebased qdev onto QOM. Since then it involves a
> conversion to string, a detour through QOM infrastructure, which (among
> other things) converts the string right back. Progress!
>
>> ... This is incredibly non-intuitive, especially given that the
>> pre-patch code performed a *similar* assignment explicitly :(
>
> So, here's my thinking process that led to this patch.
>
> To make ARM virt work, I gave myself permission to copy code from x86
> without thinking about code duplication. Once it worked, I checked what
> I actually copied. Just this loop:
>
> /* Map legacy -drive if=pflash to machine properties */
> for (i = 0; i < ARRAY_SIZE(pcms->flash); i++) {
> pflash_blk[i] = pflash_cfi01_get_blk(pcms->flash[i]);
> pflash_drv = drive_get(IF_PFLASH, 0, i);
> if (!pflash_drv) {
> continue;
> }
> loc_push_none(&loc);
> qemu_opts_loc_restore(pflash_drv->opts);
> if (pflash_blk[i]) {
> error_report("clashes with -machine");
> exit(1);
> }
> pflash_blk[i] = blk_by_legacy_dinfo(pflash_drv);
> qdev_prop_set_drive(DEVICE(pcms->flash[i]),
> "drive", pflash_blk[i], &error_fatal);
> loc_pop(&loc);
> }
>
> The easy de-dupe is to put it in a fuction like this (just for
> illustration, not even compile-tested):
>
> void pflash_cfi01_legacy_drive(PFlashCFI01 *dev[], int ndev,
> BlockBackend blk[])
> {
> int i;
> DriveInfo *dinfo;
> Location loc;
>
> // the original loop with pcms->flash replaced by dev,
> // pflash_blk by blk, pflash_cfi01_get_blk(dev[i]) by
> // dev[i]->blk, and (for good measure) pflash_drv by
> // dinfo:
> for (i = 0; i < ndev; i++) {
> blk[i] = dev[i]->blk;
> dinfo = drive_get(IF_PFLASH, 0, i);
> if (!dinfo) {
> continue;
> }
> loc_push_none(&loc);
> qemu_opts_loc_restore(dinfo->opts);
> if (blk[i]) {
> error_report("clashes with -machine");
> exit(1);
> }
> blk[i] = blk_by_legacy_dinfo(dinfo);
> qdev_prop_set_drive(DEVICE(dev[i]),
> "drive", blk[i], &error_fatal);
> loc_pop(&loc);
> }
> }
>
> Called like
>
> pflash_cfi01_legacy_drive(pcms->flash, ARRAY_SIZE(pcms->flash),
> pflash_blk);
>
> The last parameter is awkward. If you doubt me, try writing a contract.
> Further evidence: the ARM virt caller only ever uses blk[0].
>
> The awkwardness is cause by the original loop doing two things: map
> legacy -drive to properties, and collect all the BlockBackends for use
> after the loop.
>
> Better factor just the former out of the loop:
>
> pflash_cfi01_legacy_drive(pcms->flash, ARRAY_SIZE(pcms->flash));
>
> for (i = 0; i < ARRAY_SIZE(pcms->flash); i++) {
> pflash_blk[i] = pflash_cfi01_get_blk(pcms->flash[i]);
> }
>
> Now transform pflash_cfi01_legacy_drive(). First step: replace the last
> parameter by a local variable:
>
> BlockBackend *blk[ndev];
>
> Variable length array, no good. But since its only use is blk[i] in the
> loop, we can collapse it to just
>
> BlockBackend *blk;
>
> used like this:
>
> for (i = 0; i < ndev; i++) {
> blk = dev[i]->blk;
> dinfo = drive_get(IF_PFLASH, 0, i);
> if (!dinfo) {
> continue;
> }
> loc_push_none(&loc);
> qemu_opts_loc_restore(dinfo->opts);
> if (blk) {
> error_report("clashes with -machine");
> exit(1);
> }
> blk = blk_by_legacy_dinfo(dinfo);
> qdev_prop_set_drive(DEVICE(dev[i]),
> "drive", blk, &error_fatal);
> loc_pop(&loc);
> }
>
> Note that each of the two assignments to blk is used just once. Meh.
> Eliminate the variable:
>
> for (i = 0; i < ndev; i++) {
> dinfo = drive_get(IF_PFLASH, 0, i);
> if (!dinfo) {
> continue;
> }
> loc_push_none(&loc);
> qemu_opts_loc_restore(dinfo->opts);
> if (dev[i]->blk) {
> error_report("clashes with -machine");
> exit(1);
> }
> qdev_prop_set_drive(DEVICE(dev[i]), "drive",
> blk_by_legacy_dinfo(dinfo), &error_fatal);
> loc_pop(&loc);
> }
>
> And this is exactly what's in my patch.
>
>> In other words, we could have written the pre-patch (original) code like
>> this:
>>
>> diff --git a/hw/i386/pc_sysfw.c b/hw/i386/pc_sysfw.c
>> index c6285407748e..ed6e713d0982 100644
>> --- a/hw/i386/pc_sysfw.c
>> +++ b/hw/i386/pc_sysfw.c
>> @@ -291,9 +291,10 @@ void pc_system_firmware_init(PCMachineState *pcms,
>> error_report("clashes with -machine");
>> exit(1);
>> }
>> - pflash_blk[i] = blk_by_legacy_dinfo(pflash_drv);
>> qdev_prop_set_drive(DEVICE(pcms->flash[i]),
>> - "drive", pflash_blk[i], &error_fatal);
>> + "drive", blk_by_legacy_dinfo(pflash_drv),
>> + &error_fatal);
>> + pflash_blk[i] = pflash_cfi01_get_blk(pcms->flash[i]);
>> loc_pop(&loc);
>> }
>>
>> and the behavior would have been identical.
>>
>> For the sake of QOM / blk dummies like me, can you please split this
>> refactoring to a separate patch, before extracting the new function?
>
> If you think a preparatory patch is called for, I'll create one.
>
> I'd have difficulties coming up with a commit message for the one you
> proposed.
>
> I append a patch I can describe. Would it work for you?
>
>
>
> pc: Split pc_system_firmware_init()'s legacy -drive loop
>
> The loop does two things: map legacy -drive to properties, and collect
> all the backends for use after the loop. The next patch will factor
> out the former for reuse in hw/arm/virt.c. To make that easier, do
> each thing in its own loop.
>
> Signed-off-by: Markus Armbruster <arm...@redhat.com>
> ---
> hw/i386/pc_sysfw.c | 14 +++++++++-----
> 1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/hw/i386/pc_sysfw.c b/hw/i386/pc_sysfw.c
> index c628540774..90db9b57a4 100644
> --- a/hw/i386/pc_sysfw.c
> +++ b/hw/i386/pc_sysfw.c
> @@ -269,6 +269,7 @@ void pc_system_firmware_init(PCMachineState *pcms,
> {
> PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
> int i;
> + BlockBackend *blk;
> DriveInfo *pflash_drv;
> BlockBackend *pflash_blk[ARRAY_SIZE(pcms->flash)];
> Location loc;
> @@ -280,23 +281,26 @@ void pc_system_firmware_init(PCMachineState *pcms,
>
> /* Map legacy -drive if=pflash to machine properties */
> for (i = 0; i < ARRAY_SIZE(pcms->flash); i++) {
> - pflash_blk[i] = pflash_cfi01_get_blk(pcms->flash[i]);
> + blk = pflash_cfi01_get_blk(pcms->flash[i]);
> pflash_drv = drive_get(IF_PFLASH, 0, i);
> if (!pflash_drv) {
> continue;
> }
> loc_push_none(&loc);
> qemu_opts_loc_restore(pflash_drv->opts);
> - if (pflash_blk[i]) {
> + if (blk) {
> error_report("clashes with -machine");
> exit(1);
> }
> - pflash_blk[i] = blk_by_legacy_dinfo(pflash_drv);
> - qdev_prop_set_drive(DEVICE(pcms->flash[i]),
> - "drive", pflash_blk[i], &error_fatal);
> + qdev_prop_set_drive(DEVICE(pcms->flash[i]), "drive",
> + blk_by_legacy_dinfo(pflash_drv), &error_fatal);
> loc_pop(&loc);
> }
>
> + for (i = 0; i < ARRAY_SIZE(pcms->flash); i++) {
> + pflash_blk[i] = blk_by_legacy_dinfo(pflash_drv);
[*]
> + }
> +
> /* Reject gaps */
> for (i = 1; i < ARRAY_SIZE(pcms->flash); i++) {
> if (pflash_blk[i] && !pflash_blk[i - 1]) {
>
Yes, this is a huge boost to readability, as far as I'm concerned --
primarily because it kills the *second* "pflash_blk[i]" assignment in
the original loop body. Please do include this patch, and append, at once:
Reviewed-by: Laszlo Ersek <ler...@redhat.com>
... BTW: you are assigning "blk" once, and reading it once. You might as
well drop "blk" and substitute "pflash_cfi01_get_blk(pcms->flash[i])".
[*] Yes, I'm seeing your update down-thread. :)
Thanks,
Laszlo
