On Thursday 24 December 2015, Bamvor Zhang Jian wrote:
Hi, arnd
On 12/05/2015 12:44 AM, Arnd Bergmann wrote:
On Friday 04 December 2015 23:11:58 Bamvor Jian Zhang wrote:
diff --git a/drivers/char/lp.c b/drivers/char/lp.c index c4094c4..a207e0c 100644 --- a/drivers/char/lp.c +++ b/drivers/char/lp.c @@ -136,6 +136,14 @@ #include <asm/irq.h> #include <asm/uaccess.h>
+/*
- FIXME: It should be removed after COMPAT_USE_64BIT_TIME is accessible for
- 32bit architecture.
- */
+#ifndef COMPAT_USE_64BIT_TIME +#define COMPAT_USE_64BIT_TIME (0) +#endif /* COMPAT_USE_64BIT_TIME */
Unfortunately, I think this can't work: the kernel has no idea whether user space uses a 32-bit or 64-bit time_t, and we need to be able to support both kinds of user space at the same time.
What we have to do instead is change the definition of LPSETTIMEOUT, like
#if __BITS_PER_SIZE_T >= __BITS_PER_LONG #define LPSETTIMEOUT 0x060f /* set parport timeout */ #else #define LPSETTIMEOUT _IOW(0x06, 0x0f, struct timeval) #endif
We need to decide what the correct #if condition should be, but the idea is that all current user space remains unchanged, while user space built with a 64-bit time_t sees the modified definition of LPSETTIMEOUT and passes that into the kernel when using the larger structure.
I am trying to follow your suggestion. But I do not understand why `__BITS_PER_SIZE_T` is relative to sizeof(time_t). And I also tried to use `__BITS_PER_TIME_T` according to the following table.
Sorry for the confusion, I meant to write __BITS_PER_TIME_T, not __BITS_PER_SIZE_T.
- userspace | kernel | `__BITS_PER_TIME_T` | `__BITS_PER_LONG` |
`__BITS_PER_TIME_T` <= `__BITS_PER_LONG`
- -----------|----------|---------------------|-------------------|------------------------------------------
32 | 32 | 32 | 32 | true32 | 32 | 64 | 32 | false32 | 64 | 32 | 32 | true32 | 64 | 64 | 32 | false64 | 64 | 64 | 64 | true*/ #if __BITS_PER_TIME_T <= __BITS_PER_LONG #define LPSETTIMEOUT 0x060f /* set parport timeout */ #else #define LPSETTIMEOUT _IOW(0x06, 0x0f, struct timeval) #endif
As you know, there is no `__BITS_PER_TIME_T` as well. Finally, I thought I could make use of `__USE_TIME_BITS64` which mentioned in https://sourceware.org/glibc/wiki/Y2038ProofnessDesign
How about something like this?
#if defined(__USE_TIME_BITS64) && __BITS_PER_LONG == 32 #define LPSETTIMEOUT _IOW(0x06, 0x0f, struct timeval) #else #define LPSETTIMEOUT 0x060f /* set parport timeout */ #endif
Yes, this is what I meant. Unfortunately, we have not agreed on what we are going to call that macro, but this is roughly how it should work. However, the definition you have here is only correct for user space, not for the kernel itself, which needs a slightly different definition when __KERNEL__ is defined and 'struct timeval' has been removed from the kernel.
Arnd