Re: [Qemu-devel] [PATCH v2] linux-user: Allow getdents to be provided by getdents64

[Claudio Fontana]

On 04.06.2013 13:12, Peter Maydell wrote:
> Newer architectures may only implement the getdents64 syscall, not
> getdents. Provide an implementation of getdents in terms of getdents64
> so that we can run getdents-using targets on a getdents64-only host.
> 
> Signed-off-by: Peter Maydell <address@hidden>
> Message-id: address@hidden
> ---
> Changes v1->v2:
>  * memmove() call moved to before we write inode/offset/reclen
>  * wrapped a stray long line that snuck in somehow
> 
>  linux-user/syscall.c |   61 
> +++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 60 insertions(+), 1 deletion(-)
> 

I tested the change, and it works, however I get this during compilation:

linux-user/syscall.c:382:12: warning: 'sys_futimesat' defined but not used 
[-Wunused-function]

> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 0099d64..4151c78 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -223,8 +223,11 @@ static int gettid(void) {
>      return -ENOSYS;
>  }
>  #endif
> +#ifdef __NR_getdents
>  _syscall3(int, sys_getdents, uint, fd, struct linux_dirent *, dirp, uint, 
> count);
> -#if defined(TARGET_NR_getdents64) && defined(__NR_getdents64)
> +#endif
> +#if !defined(__NR_getdents) || \
> +    (defined(TARGET_NR_getdents64) && defined(__NR_getdents64))
>  _syscall3(int, sys_getdents64, uint, fd, struct linux_dirent64 *, dirp, 
> uint, count);
>  #endif
>  #if defined(TARGET_NR__llseek) && defined(__NR_llseek)
> @@ -7123,6 +7126,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
> arg1,
>          break;
>  #endif
>      case TARGET_NR_getdents:
> +#ifdef __NR_getdents
>  #if TARGET_ABI_BITS == 32 && HOST_LONG_BITS == 64
>          {
>              struct target_dirent *target_dirp;
> @@ -7195,6 +7199,61 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
> arg1,
>              unlock_user(dirp, arg2, ret);
>          }
>  #endif
> +#else
> +        /* Implement getdents in terms of getdents64 */
> +        {
> +            struct linux_dirent64 *dirp;
> +            abi_long count = arg3;
> +
> +            dirp = lock_user(VERIFY_WRITE, arg2, count, 0);
> +            if (!dirp) {
> +                goto efault;
> +            }
> +            ret = get_errno(sys_getdents64(arg1, dirp, count));
> +            if (!is_error(ret)) {
> +                /* Convert the dirent64 structs to target dirent.  We do this
> +                 * in-place, since we can guarantee that a target_dirent is 
> no
> +                 * larger than a dirent64; however this means we have to be
> +                 * careful to read everything before writing in the new 
> format.
> +                 */
> +                struct linux_dirent64 *de;
> +                struct target_dirent *tde;
> +                int len = ret;
> +                int tlen = 0;
> +
> +                de = dirp;
> +                tde = (struct target_dirent *)dirp;
> +                while (len > 0) {
> +                    int namelen, treclen;
> +                    int reclen = de->d_reclen;
> +                    uint64_t ino = de->d_ino;
> +                    int64_t off = de->d_off;
> +                    uint8_t type = de->d_type;
> +
> +                    namelen = strlen(de->d_name);
> +                    treclen = offsetof(struct target_dirent, d_name)
> +                        + namelen + 2;
> +                    treclen = QEMU_ALIGN_UP(treclen, sizeof(abi_long));
> +
> +                    memmove(tde->d_name, de->d_name, namelen + 1);
> +                    tde->d_ino = tswapal(ino);
> +                    tde->d_off = tswapal(off);
> +                    tde->d_reclen = tswap16(treclen);
> +                    /* The target_dirent type is in what was formerly a 
> padding
> +                     * byte at the end of the structure:
> +                     */
> +                    *(((char *)tde) + treclen - 1) = type;
> +
> +                    de = (struct linux_dirent64 *)((char *)de + reclen);
> +                    tde = (struct target_dirent *)((char *)tde + treclen);
> +                    len -= reclen;
> +                    tlen += treclen;
> +                }
> +                ret = tlen;
> +            }
> +            unlock_user(dirp, arg2, ret);
> +        }
> +#endif
>          break;
>  #if defined(TARGET_NR_getdents64) && defined(__NR_getdents64)
>      case TARGET_NR_getdents64:
> 


-- 
Claudio Fontana
Server OS Architect
Huawei Technologies Duesseldorf GmbH
Riesstraße 25 - 80992 München

office: +49 89 158834 4135
mobile: +49 15253060158