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Re: [PATCH 2/5][TAKE2] fallocate() on s390 - glibc wrapper

To: torvalds@xxxxxxxx, akpm@xxxxxxxxxxxxxxxxxxxx
Subject: Re: [PATCH 2/5][TAKE2] fallocate() on s390 - glibc wrapper
From: "Amit K. Arora" <aarora@xxxxxxxxxxxxxxxxxx>
Date: Mon, 14 May 2007 21:03:30 +0530
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, suparna@xxxxxxxxxx, cmm@xxxxxxxxxx
In-reply-to: <20070514144833.GB31748@amitarora.in.ibm.com>
References: <20070330071417.GI355@devserv.devel.redhat.com> <20070417125514.GA7574@amitarora.in.ibm.com> <20070418130600.GW5967@schatzie.adilger.int> <20070420135146.GA21352@amitarora.in.ibm.com> <20070420145918.GY355@devserv.devel.redhat.com> <20070424121632.GA10136@amitarora.in.ibm.com> <20070426175056.GA25321@amitarora.in.ibm.com> <20070514132926.GA30768@amitarora.in.ibm.com> <20070514142820.GA31468@amitarora.in.ibm.com> <20070514144833.GB31748@amitarora.in.ibm.com>
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On Mon, May 14, 2007 at 08:18:34PM +0530, Amit K. Arora wrote:
> This is the patch suggested by Martin Schwidefsky. Here are the comments
> and patch from him.

Martin also suggested a wrapper in glibc to handle this system call on
s390. Posting it here so that we get feedback for this too.
Here it is:

.globl __fallocate
ENTRY(__fallocate)
        stm     %r6,%r7,28(%r15)        /* save %r6/%r7 on stack */
        cfi_offset (%r7, -68)
        cfi_offset (%r6, -72)
        lm      %r6,%r7,96(%r15)        /* load loff_t len from stack */
        svc     SYS_ify(fallocate)
        lm      %r6,%r7,28(%r15)        /* restore %r6/%r7 from stack */
        br      %r14
PSEUDO_END(__fallocate)

--
Regards,
Amit Arora
 
> -------------
> From: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
> 
> This patch implements support of fallocate system call on s390(x)
> platform. A wrapper is added to address the issue which s390 ABI has
> with the arguments of this system call.
> 
> Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
> ---
> 
>  arch/s390/kernel/compat_wrapper.S |   10 ++++++++++
>  arch/s390/kernel/sys_s390.c       |   29 +++++++++++++++++++++++++++++
>  arch/s390/kernel/syscalls.S       |    1 +
>  include/asm-s390/unistd.h         |    3 ++-
>  4 files changed, 42 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6.21/arch/s390/kernel/compat_wrapper.S
> ===================================================================
> --- linux-2.6.21.orig/arch/s390/kernel/compat_wrapper.S
> +++ linux-2.6.21/arch/s390/kernel/compat_wrapper.S
> @@ -1682,3 +1682,13 @@ compat_sys_utimes_wrapper:
>       llgtr   %r2,%r2                 # char *
>       llgtr   %r3,%r3                 # struct compat_timeval *
>       jg      compat_sys_utimes
> +
> +     .globl  sys_fallocate_wrapper
> +sys_fallocate_wrapper:
> +     lgfr    %r2,%r2                 # int
> +     lgfr    %r3,%r3                 # int
> +     sllg    %r4,%r4,32              # get high word of 64bit loff_t
> +     lr      %r4,%r5                 # get low word of 64bit loff_t
> +     sllg    %r5,%r6,32              # get high word of 64bit loff_t
> +     l       %r5,164(%r15)           # get low word of 64bit loff_t
> +     jg      sys_fallocate
> Index: linux-2.6.21/arch/s390/kernel/syscalls.S
> ===================================================================
> --- linux-2.6.21.orig/arch/s390/kernel/syscalls.S
> +++ linux-2.6.21/arch/s390/kernel/syscalls.S
> @@ -322,3 +322,4 @@ NI_SYSCALL                                                
>         /* 310 sys_move_pages *
>  SYSCALL(sys_getcpu,sys_getcpu,sys_getcpu_wrapper)
>  SYSCALL(sys_epoll_pwait,sys_epoll_pwait,compat_sys_epoll_pwait_wrapper)
>  SYSCALL(sys_utimes,sys_utimes,compat_sys_utimes_wrapper)
> +SYSCALL(s390_fallocate,sys_fallocate,sys_fallocate_wrapper)
> Index: linux-2.6.21/arch/s390/kernel/sys_s390.c
> ===================================================================
> --- linux-2.6.21.orig/arch/s390/kernel/sys_s390.c
> +++ linux-2.6.21/arch/s390/kernel/sys_s390.c
> @@ -286,3 +286,32 @@ int kernel_execve(const char *filename, 
>                 "d" (__arg3) : "memory");
>       return __svcres;
>  }
> +
> +#ifndef CONFIG_64BIT
> +/*
> + * This is a wrapper to call sys_fallocate(). For 31 bit s390 the last
> + * 64 bit argument "len" is split into the upper and lower 32 bits. The
> + * system call wrapper in the user space loads the value to %r6/%r7.
> + * The code in entry.S keeps the values in %r2 - %r6 where they are and
> + * stores %r7 to 96(%r15). But the standard C linkage requires that
> + * the whole 64 bit value for len is stored on the stack and doesn't
> + * use %r6 at all. So s390_fallocate has to convert the arguments from
> + *   %r2: fd, %r3: mode, %r4/%r5: offset, %r6/96(%r15)-99(%r15): len
> + * to
> + *   %r2: fd, %r3: mode, %r4/%r5: offset, 96(%r15)-103(%r15): len
> + */
> +asmlinkage long s390_fallocate(int fd, int mode, loff_t offset,
> +                            u32 len_high, u32 len_low)
> +{
> +     union {
> +             u64 len;
> +             struct {
> +                     u32 high;
> +                     u32 low;
> +             };
> +     } cv;
> +     cv.high = len_high;
> +     cv.low = len_low;
> +     return sys_fallocate(fd, mode, offset, cv.len);
> +}
> +#endif
> Index: linux-2.6.21/include/asm-s390/unistd.h
> ===================================================================
> --- linux-2.6.21.orig/include/asm-s390/unistd.h
> +++ linux-2.6.21/include/asm-s390/unistd.h
> @@ -251,8 +251,9 @@
>  #define __NR_getcpu          311
>  #define __NR_epoll_pwait     312
>  #define __NR_utimes          313
> +#define __NR_fallocate               314
> 
> -#define NR_syscalls 314
> +#define NR_syscalls 315
> 
>  /* 
>   * There are some system calls that are not present on 64 bit, some
> -
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