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Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_c
From: |
Eduardo Habkost |
Subject: |
Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers |
Date: |
Fri, 7 Jul 2017 10:13:00 -0300 |
User-agent: |
Mutt/1.8.0 (2017-02-23) |
On Fri, Jul 07, 2017 at 01:33:20PM +0200, Igor Mammedov wrote:
> On Tue, 4 Jul 2017 19:08:44 +0100
> Mark Cave-Ayland <address@hidden> wrote:
>
> > On 03/07/17 10:39, Igor Mammedov wrote:
> >
> > > On Thu, 29 Jun 2017 15:07:19 +0100
> > > Mark Cave-Ayland <address@hidden> wrote:
> > >
> > >> When looking to instantiate a TYPE_FW_CFG_MEM or TYPE_FW_CFG_IO device
> > >> to be
> > >> able to wire it up differently, it is much more convenient for the
> > >> caller to
> > >> instantiate the device and have the fw_cfg default files already
> > >> preloaded
> > >> during realize.
> > >>
> > >> Move fw_cfg_init1() to the end of both the fw_cfg_mem_realize() and
> > >> fw_cfg_io_realize() functions so it no longer needs to be called manually
> > >> when instantiating the device, and also rename it to
> > >> fw_cfg_common_realize()
> > >> which better describes its new purpose.
> > >>
> > >> Since it is now the responsibility of the machine to wire up the fw_cfg
> > >> device
> > >> it is necessary to introduce a object_property_add_child() call into
> > >> fw_cfg_init_io() and fw_cfg_init_mem() to link the fw_cfg device to the
> > >> root
> > >> machine object as before.
> > >>
> > >> Finally we can now convert the asserts() preventing multiple fw_cfg
> > >> devices
> > >> and unparented fw_cfg devices being instantiated and replace them with
> > >> proper
> > >> error reporting at realize time. This allows us to remove FW_CFG_NAME and
> > >> FW_CFG_PATH since they are no longer required.
> > >>
> > >> Signed-off-by: Mark Cave-Ayland <address@hidden>
> > >> ---
> > >> hw/nvram/fw_cfg.c | 41 +++++++++++++++++++++++++++++------------
> > >> 1 file changed, 29 insertions(+), 12 deletions(-)
> > >>
> > >> diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
> > >> index 2291121..31029ac 100644
> > >> --- a/hw/nvram/fw_cfg.c
> > >> +++ b/hw/nvram/fw_cfg.c
> > >> @@ -37,9 +37,6 @@
> > >>
> > >> #define FW_CFG_FILE_SLOTS_DFLT 0x20
> > >>
> > >> -#define FW_CFG_NAME "fw_cfg"
> > >> -#define FW_CFG_PATH "/machine/" FW_CFG_NAME
> > >> -
> > >> #define TYPE_FW_CFG "fw_cfg"
> > >> #define TYPE_FW_CFG_IO "fw_cfg_io"
> > >> #define TYPE_FW_CFG_MEM "fw_cfg_mem"
> > >> @@ -920,19 +917,22 @@ static int fw_cfg_unattached_at_realize(void)
> > >> }
> > >>
> > >>
> > >> -static void fw_cfg_init1(DeviceState *dev)
> > >> +static void fw_cfg_common_realize(DeviceState *dev, Error **errp)
> > >> {
> > >> FWCfgState *s = FW_CFG(dev);
> > >> MachineState *machine = MACHINE(qdev_get_machine());
> > >> uint32_t version = FW_CFG_VERSION;
> > >>
> > >> - assert(!object_resolve_path(FW_CFG_PATH, NULL));
> > >> -
> > >> - object_property_add_child(OBJECT(machine), FW_CFG_NAME, OBJECT(s),
> > >> NULL);
> > >> -
> > >> - qdev_init_nofail(dev);
> > >> + if (!fw_cfg_find()) {
> > > maybe add comment that here, that fw_cfg_find() will return NULL if more
> > > than
> > > 1 device is found.
> >
> > This should be the same behaviour as before, i.e. a NULL means that the
> > fw_cfg device couldn't be found. It seems intuitive to me from the name
> > of the function exactly what it does, so I don't find the lack of
> > comment too confusing. Does anyone else have any thoughts here?
> intuitive meaning from the function name would be return NULL if nothing were
> found,
> however it's not the case here.
>
> taking in account that fwcfg in not user creatable device how about:
>
> diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
> index 316fca9..8f6eef8 100644
> --- a/hw/nvram/fw_cfg.c
> +++ b/hw/nvram/fw_cfg.c
> @@ -1014,7 +1014,10 @@ FWCfgState *fw_cfg_init_mem(hwaddr ctl_addr, hwaddr
> data_addr)
>
> FWCfgState *fw_cfg_find(void)
> {
> - return FW_CFG(object_resolve_path(FW_CFG_PATH, NULL));
> + bool ambig = false;
> + FWCfgState *f = FW_CFG(object_resolve_path_type("", TYPE_FW_CFG,
> &ambig));
> + assert(!ambig);
> + return f;
> }
>
> or if we must to print user friendly error and fail realize gracefully
> (not sure why) just add errp argument to function so it could report
> error back to caller, then places that do not care much about graceful
> exit would use error_abort as argument and realize would use
> its local_error/errp argument.
I don't disagree with adding the assert(), but it looks like
making fw_cfg_find() return NULL if there are multiple devices
can be useful for realize.
In this case, it looks like Mark is relying on that in
fw_cfg_common_realize(): if multiple devices are created,
fw_cfg_find() will return NULL, and realize will fail. This
sounds like a more graceful way to handle multiple-device
creation than crashing on fw_cfg_find(). This is the solution
used by find_vmgenid_dev()/vmgenid_realize(), BTW.
Either way, we have to choose: either we make fw_cfg_find() crash
when multiple devices exist (in this case, the fw_cfg_find() call
on realize will be useless), or we make it return NULL and
document it very clearly.
>
>
> > >> + error_setg(errp, "at most one %s device is permitted",
> > >> TYPE_FW_CFG);
> > > s/TYPE_FW_CFG/object_get_typename()/
> > > so it would print leaf type name
I disagree. We allow at most one fw_cfg device (it doesn't
matter which type), not at most one device of each leaf type.
Saying "at most one fw_cfg_mem device is permitted" if 1
fw_cfg_io and 1 fw_cfg_mem device is created would be misleading.
> >
> > Previously the code would add the device to the machine at FW_CFG_PATH
> > which was fixed at /machine/fw_cfg regardless of whether it was
> > fw_cfg_io or fw_cfg_mem type (see the top of fw_cfg.c).
> >
> > This was a deliberate attempt to preserve the existing behaviour and if
> > we were to give the leaf type name I think this would be misleading,
> > since it implies you could have one fw_cfg_io and one fw_cfg_mem which
> > isn't correct.
> I don't have strong preference here, considering that it's
> hardcoded in board (not user specified) device,
> developer that stumbles upon error should be able to dig out which
> concrete type caused it.
>
> > >> + return;
> > >> + }
> > >>
> > >> - assert(!fw_cfg_unattached_at_realize());
> > >> + if (fw_cfg_unattached_at_realize()) {
> > > as I pointed out in v6, this condition will always be false,
> > > I suggest to drop 4/6 patch and this hunk here so it won't to confuse
> > > readers with assumption that condition might succeed.
> >
> > Definitely look more closely at the fw_cfg_unattached_at_realize()
> > implementation in patch 4. You'll see that the check to determine if the
> > device is attached does not check obj->parent but checks to see if the
> > device exists under /machine/unattached which is what the
> > device_set_realised() does if the device doesn't have a parent.
> looking more fw_cfg_unattached_at_realize(),
> returns true if fwcfg is direct child of/machine/unattached
> meaning implicit parent assignment.
>
> As result, above condition essentially forbids having fwcfg under
> /machine/unattached and forces user to explicitly set parent
> outside of /machine/unattached or be a child of some other device.
>
> Is this your intent (why)?
I'm confused by this part as well. I still don't see the point
of fw_cfg_unattached_at_realize(), I need to re-read the patches
and commit messages to try to understand that.
If we are changing fw_cfg_find() to not care about the fw_cfg
device location, we don't need to care if it's in
/machine/unattached or not.
> [...]
--
Eduardo
- Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers, (continued)
- Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers, Igor Mammedov, 2017/07/07
- Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers, Eduardo Habkost, 2017/07/07
- Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers, Eduardo Habkost, 2017/07/07
- Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers, Mark Cave-Ayland, 2017/07/07
- Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers, Igor Mammedov, 2017/07/10
- Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers, Eduardo Habkost, 2017/07/10
- Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers, Igor Mammedov, 2017/07/10
- Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers, Eduardo Habkost, 2017/07/10
- Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers,
Eduardo Habkost <=
- Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers, Igor Mammedov, 2017/07/07
- Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers, Eduardo Habkost, 2017/07/07
- Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers, Igor Mammedov, 2017/07/07
- Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers, Eduardo Habkost, 2017/07/07
- Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers, Eduardo Habkost, 2017/07/07
- Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers, Laszlo Ersek, 2017/07/07
- Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers, Mark Cave-Ayland, 2017/07/07