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]) {
--
2.17.2
