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    Subject[PATCH 2/5][TAKE3] fallocate() on s390
    This is the patch suggested by Martin Schwidefsky to support
    sys_fallocate() on s390(x) platform.

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

    .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)


    Here are the comments and the patch to linux kernel from him.

    -------------
    From: Martin Schwidefsky <schwidefsky@de.ibm.com>

    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@de.ibm.com>
    ---
    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-2.6.22-rc1/arch/s390/kernel/compat_wrapper.S
    ===================================================================
    --- linux-2.6.22-rc1.orig/arch/s390/kernel/compat_wrapper.S
    +++ linux-2.6.22-rc1/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-2.6.22-rc1/arch/s390/kernel/sys_s390.c
    ===================================================================
    --- linux-2.6.22-rc1.orig/arch/s390/kernel/sys_s390.c
    +++ linux-2.6.22-rc1/arch/s390/kernel/sys_s390.c
    @@ -265,3 +265,32 @@ s390_fadvise64_64(struct fadvise64_64_ar
    return -EFAULT;
    return sys_fadvise64_64(a.fd, a.offset, a.len, a.advice);
    }
    +
    +#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-2.6.22-rc1/arch/s390/kernel/syscalls.S
    ===================================================================
    --- linux-2.6.22-rc1.orig/arch/s390/kernel/syscalls.S
    +++ linux-2.6.22-rc1/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-2.6.22-rc1/include/asm-s390/unistd.h
    ===================================================================
    --- linux-2.6.22-rc1.orig/include/asm-s390/unistd.h
    +++ linux-2.6.22-rc1/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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