Sometimes we use the 'struct' keyword to help us reduce
dependencies between header files. Document that practice.
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
I wonder if this is too terse? Should we give examples?
---
HACKING | 2 ++
1 file changed, 2 insertions(+)
diff --git a/HACKING b/HACKING
index 0fc3e0fc04..112685bdaf 100644
--- a/HACKING
+++ b/HACKING
@@ -101,6 +101,8 @@ it points to, or it is aliased to another pointer that is.
2.3. Typedefs
Typedefs are used to eliminate the redundant 'struct' keyword.
+However, the 'struct' keyword may be sometimes used in header
+files to avoid unnecessary dependencies between headers.
2.4. Reserved namespaces in C and POSIX
Underscore capital, double underscore, and underscore 't' suffixes should be
--
2.21.0
On 7/30/19 4:07 PM, Eduardo Habkost wrote: > Sometimes we use the 'struct' keyword to help us reduce > dependencies between header files. Document that practice. > > Signed-off-by: Eduardo Habkost <ehabkost@redhat.com> > --- > I wonder if this is too terse? Should we give examples? An example might be nice, but I like the wording - it makes it obvious that the header uses 'struct' but the .c should use the typedef. > --- > HACKING | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/HACKING b/HACKING > index 0fc3e0fc04..112685bdaf 100644 > --- a/HACKING > +++ b/HACKING > @@ -101,6 +101,8 @@ it points to, or it is aliased to another pointer that is. > > 2.3. Typedefs > Typedefs are used to eliminate the redundant 'struct' keyword. > +However, the 'struct' keyword may be sometimes used in header > +files to avoid unnecessary dependencies between headers. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
On 30/07/2019 23.07, Eduardo Habkost wrote: > Sometimes we use the 'struct' keyword to help us reduce > dependencies between header files. Document that practice. > > Signed-off-by: Eduardo Habkost <ehabkost@redhat.com> > --- > I wonder if this is too terse? Should we give examples? > --- > HACKING | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/HACKING b/HACKING > index 0fc3e0fc04..112685bdaf 100644 > --- a/HACKING > +++ b/HACKING > @@ -101,6 +101,8 @@ it points to, or it is aliased to another pointer that is. > > 2.3. Typedefs > Typedefs are used to eliminate the redundant 'struct' keyword. > +However, the 'struct' keyword may be sometimes used in header > +files to avoid unnecessary dependencies between headers. See also the discussion earlier this year: https://www.mail-archive.com/qemu-devel@nongnu.org/msg586180.html ... and we should merge HACKING and CODING_STYLE finally (that was on my private TODO list, but I never found the time to do it). Thomas
On Wed, Jul 31, 2019 at 10:35:31AM +0200, Thomas Huth wrote:
> On 30/07/2019 23.07, Eduardo Habkost wrote:
> > Sometimes we use the 'struct' keyword to help us reduce
> > dependencies between header files. Document that practice.
> >
> > Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
> > ---
> > I wonder if this is too terse? Should we give examples?
> > ---
> > HACKING | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/HACKING b/HACKING
> > index 0fc3e0fc04..112685bdaf 100644
> > --- a/HACKING
> > +++ b/HACKING
> > @@ -101,6 +101,8 @@ it points to, or it is aliased to another pointer that is.
> >
> > 2.3. Typedefs
> > Typedefs are used to eliminate the redundant 'struct' keyword.
> > +However, the 'struct' keyword may be sometimes used in header
> > +files to avoid unnecessary dependencies between headers.
>
> See also the discussion earlier this year:
>
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg586180.html
Nice, it adds even more information than this patch.
For reference, this is the patch at the URL above:
-Typedefs are used to eliminate the redundant 'struct' keyword.
+Typedefs can be used to eliminate the redundant 'struct' keyword. This is
+especially helpful for common types that are used all over the place. Since
+certain C compilers choke on duplicated typedefs, you should avoid them and
+declare a typedef only in one header file. For common types, you can use
+"include/qemu/typedefs.h" for example. Note that it is also perfectly fine to
+use forward struct definitions without typedefs for references in headers
+to avoid the problem with duplicated typedefs.
I don't agree with the first two sentences, and I agree with what Paolo said
here:
https://www.mail-archive.com/qemu-devel@nongnu.org/msg586214.html
("I agree 100% with the wording after 'Since'. However, I think the first
part should be made stronger, not weaker.")
Paolo sent the following proposal:
| Typedefs are use to eliminate the redundant 'struct' keyword, since type
| names have a different style than other identifiers ("CamelCase" versus
| "snake_case"). Each struct should have a CamelCase name and a
| corresponding typedef.
|
| Since certain C compilers choke on duplicated typedefs, you should avoid
| them and declare a typedef only in one header file. For common types,
| you can use "include/qemu/typedefs.h" for example. However, as a metter
| of convenience it is also perfectly fine to use forward struct
| definitions instead of typedefs in headers and function prototypes; this
| avoids problems with duplicated typedefs and reduces the need to include
| headers from other headers.
It seems perfect to me.
Paolo, do I have your signed-off-by to send that in a patch?
>
> ... and we should merge HACKING and CODING_STYLE finally (that was on my
> private TODO list, but I never found the time to do it).
Agreed, but I prefer to fix one problem at a time.
--
Eduardo
On 01/08/19 20:50, Eduardo Habkost wrote:
> On Wed, Jul 31, 2019 at 10:35:31AM +0200, Thomas Huth wrote:
>> On 30/07/2019 23.07, Eduardo Habkost wrote:
>>> Sometimes we use the 'struct' keyword to help us reduce
>>> dependencies between header files. Document that practice.
>>>
>>> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
>>> ---
>>> I wonder if this is too terse? Should we give examples?
>>> ---
>>> HACKING | 2 ++
>>> 1 file changed, 2 insertions(+)
>>>
>>> diff --git a/HACKING b/HACKING
>>> index 0fc3e0fc04..112685bdaf 100644
>>> --- a/HACKING
>>> +++ b/HACKING
>>> @@ -101,6 +101,8 @@ it points to, or it is aliased to another pointer that is.
>>>
>>> 2.3. Typedefs
>>> Typedefs are used to eliminate the redundant 'struct' keyword.
>>> +However, the 'struct' keyword may be sometimes used in header
>>> +files to avoid unnecessary dependencies between headers.
>>
>> See also the discussion earlier this year:
>>
>> https://www.mail-archive.com/qemu-devel@nongnu.org/msg586180.html
>
> Nice, it adds even more information than this patch.
>
> For reference, this is the patch at the URL above:
>
> -Typedefs are used to eliminate the redundant 'struct' keyword.
> +Typedefs can be used to eliminate the redundant 'struct' keyword. This is
> +especially helpful for common types that are used all over the place. Since
> +certain C compilers choke on duplicated typedefs, you should avoid them and
> +declare a typedef only in one header file. For common types, you can use
> +"include/qemu/typedefs.h" for example. Note that it is also perfectly fine to
> +use forward struct definitions without typedefs for references in headers
> +to avoid the problem with duplicated typedefs.
>
> I don't agree with the first two sentences, and I agree with what Paolo said
> here:
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg586214.html
>
> ("I agree 100% with the wording after 'Since'. However, I think the first
> part should be made stronger, not weaker.")
>
> Paolo sent the following proposal:
>
> | Typedefs are use to eliminate the redundant 'struct' keyword, since type
> | names have a different style than other identifiers ("CamelCase" versus
> | "snake_case"). Each struct should have a CamelCase name and a
> | corresponding typedef.
> |
> | Since certain C compilers choke on duplicated typedefs, you should avoid
> | them and declare a typedef only in one header file. For common types,
> | you can use "include/qemu/typedefs.h" for example. However, as a metter
> | of convenience it is also perfectly fine to use forward struct
> | definitions instead of typedefs in headers and function prototypes; this
> | avoids problems with duplicated typedefs and reduces the need to include
> | headers from other headers.
>
> It seems perfect to me.
>
> Paolo, do I have your signed-off-by to send that in a patch?
Sure.
Paolo
On 01/08/2019 21.23, Paolo Bonzini wrote:
> On 01/08/19 20:50, Eduardo Habkost wrote:
>> On Wed, Jul 31, 2019 at 10:35:31AM +0200, Thomas Huth wrote:
>>> On 30/07/2019 23.07, Eduardo Habkost wrote:
>>>> Sometimes we use the 'struct' keyword to help us reduce
>>>> dependencies between header files. Document that practice.
>>>>
>>>> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
>>>> ---
>>>> I wonder if this is too terse? Should we give examples?
>>>> ---
>>>> HACKING | 2 ++
>>>> 1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/HACKING b/HACKING
>>>> index 0fc3e0fc04..112685bdaf 100644
>>>> --- a/HACKING
>>>> +++ b/HACKING
>>>> @@ -101,6 +101,8 @@ it points to, or it is aliased to another pointer that is.
>>>>
>>>> 2.3. Typedefs
>>>> Typedefs are used to eliminate the redundant 'struct' keyword.
>>>> +However, the 'struct' keyword may be sometimes used in header
>>>> +files to avoid unnecessary dependencies between headers.
>>>
>>> See also the discussion earlier this year:
>>>
>>> https://www.mail-archive.com/qemu-devel@nongnu.org/msg586180.html
>>
>> Nice, it adds even more information than this patch.
>>
>> For reference, this is the patch at the URL above:
>>
>> -Typedefs are used to eliminate the redundant 'struct' keyword.
>> +Typedefs can be used to eliminate the redundant 'struct' keyword. This is
>> +especially helpful for common types that are used all over the place. Since
>> +certain C compilers choke on duplicated typedefs, you should avoid them and
>> +declare a typedef only in one header file. For common types, you can use
>> +"include/qemu/typedefs.h" for example. Note that it is also perfectly fine to
>> +use forward struct definitions without typedefs for references in headers
>> +to avoid the problem with duplicated typedefs.
>>
>> I don't agree with the first two sentences, and I agree with what Paolo said
>> here:
>> https://www.mail-archive.com/qemu-devel@nongnu.org/msg586214.html
>>
>> ("I agree 100% with the wording after 'Since'. However, I think the first
>> part should be made stronger, not weaker.")
>>
>> Paolo sent the following proposal:
>>
>> | Typedefs are use to eliminate the redundant 'struct' keyword, since type
s/use/used/
>> | names have a different style than other identifiers ("CamelCase" versus
>> | "snake_case"). Each struct should have a CamelCase name and a
>> | corresponding typedef.
>> |
>> | Since certain C compilers choke on duplicated typedefs, you should avoid
>> | them and declare a typedef only in one header file. For common types,
>> | you can use "include/qemu/typedefs.h" for example. However, as a metter
s/metter/matter/
>> | of convenience it is also perfectly fine to use forward struct
>> | definitions instead of typedefs in headers and function prototypes; this
>> | avoids problems with duplicated typedefs and reduces the need to include
>> | headers from other headers.
With the typos fixed:
Reviewed-by: Thomas Huth <thuth@redhat.com>
On Tue, Jul 30, 2019 at 11:07 PM Eduardo Habkost <ehabkost@redhat.com> wrote: > Sometimes we use the 'struct' keyword to help us reduce > dependencies between header files. Document that practice. > > Signed-off-by: Eduardo Habkost <ehabkost@redhat.com> > --- > I wonder if this is too terse? Should we give examples? > --- > I am inclined to have the judgement very similar to Eric's - it seems to me the change is fine as is, so: Reviewed-by: Aleksandar Markovic <amarkovic@wavecomp.com> > HACKING | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/HACKING b/HACKING > index 0fc3e0fc04..112685bdaf 100644 > --- a/HACKING > +++ b/HACKING > @@ -101,6 +101,8 @@ it points to, or it is aliased to another pointer that > is. > > 2.3. Typedefs > Typedefs are used to eliminate the redundant 'struct' keyword. > +However, the 'struct' keyword may be sometimes used in header > +files to avoid unnecessary dependencies between headers. > > 2.4. Reserved namespaces in C and POSIX > Underscore capital, double underscore, and underscore 't' suffixes should > be > -- > 2.21.0 > >
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