On Mon, 1 May 2006, Alexey Dobriyan wrote:
> On Mon, May 01, 2006 at 04:00:09PM +0200, Jan Engelhardt wrote:
>>> +Please don't use things like "vps_t".
>>> +It's a _mistake_ to use typedef for structures and pointers. When you see a
>>> + vps_t a;
>>> +in the source, what does it mean?
>>> +In contrast, if it says
>>> + struct virtual_container *a;
>>> +you can actually tell what "a" is.
>>> +
>>> +Lots of people think that typedefs "help readability". Not so. They are
>>> +useful only for:
>> [...]
>>
>> What about task_t vs struct task_struct? Both are used in the kernel.
>
> task_t => struct task
> struct task_struct => struct task
>
> Roughly 2765 hits :-\
Yes, also 'current' is probably the most used. Any, since this
has become a FAQ, maybe it's about time to put something in the
Documentation?
--- /usr/src/linux-2.6.16.4/Documentation/CodingStyle.orig 2006-05-01 10:17:03.000000000 -0400
+++ /usr/src/linux-2.6.16.4/Documentation/CodingStyle 2006-05-01 10:37:09.000000000 -0400
@@ -343,6 +343,33 @@
Remember: if another thread can find your data structure, and you don't
have a reference count on it, you almost certainly have a bug.
+ typedefs and and structs
+
+Typedefs should never be used for information hiding. In other words,
+if a typedef defines an aggregate type, and the individual components
+are accessed anywhere in the code, a typedef should not be used.
+
+An example of proper usage:
+typedef struct opaque_type FILE; // In a header
+
+ FILE *fp; // In a program block
+
+The type 'FILE' in this example is something that was defined in
+a 'C' runtime library. The code uses pointers to this opaque type,
+but never even knows, and doesn't care, what's inside that structure.
+Therefore, FILE can have been defined using a typedef.
+
+An example of incorrect usage:
+
+typedef struct file_operations FO; // In a header
+
+ FO fo; // In a program block
+ memset(&foo, 0x00, sizeof(foo));
+
+In this case, object FO contains structure members that will be
+accessed by the code. It should not have been defined. Instead,
+the structure name should have been used directly.
+
Chapter 11: Macros, Enums and RTL
In case the M$ server mangles the patch, it's included as an attachment.
Cheers,
Dick Johnson
Penguin : Linux version 2.6.16.4 on an i686 machine (5592.89 BogoMips).
New book: http://www.lymanschool.com
_
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--- /usr/src/linux-2.6.16.4/Documentation/CodingStyle.orig 2006-05-01 10:17:03.000000000 -0400
+++ /usr/src/linux-2.6.16.4/Documentation/CodingStyle 2006-05-01 10:37:09.000000000 -0400
@@ -343,6 +343,33 @@
Remember: if another thread can find your data structure, and you don't
have a reference count on it, you almost certainly have a bug.
+ typedefs and and structs
+
+Typedefs should never be used for information hiding. In other words,
+if a typedef defines an aggregate type, and the individual components
+are accessed anywhere in the code, a typedef should not be used.
+
+An example of proper usage:
+typedef struct opaque_type FILE; // In a header
+
+ FILE *fp; // In a program block
+
+The type 'FILE' in this example is something that was defined in
+a 'C' runtime library. The code uses pointers to this opaque type,
+but never even knows, and doesn't care, what's inside that structure.
+Therefore, FILE can have been defined using a typedef.
+
+An example of incorrect usage:
+
+typedef struct file_operations FO; // In a header
+
+ FO fo; // In a program block
+ memset(&foo, 0x00, sizeof(foo));
+
+In this case, object FO contains structure members that will be
+accessed by the code. It should not have been defined. Instead,
+the structure name should have been used directly.
+
Chapter 11: Macros, Enums and RTL
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