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

[Laurent Vivier <laurent@vivier.eu>]

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Tested on m68k on x86_64 as described in the patch comment, in a a debian-etch
linux container.

Works fine, except the drec_len differs between getdents() and getdents64().

See comment below.

> Le 2 juin 2013 à 19:10, Peter Maydell <peter.maydell@linaro.org> a écrit :
>
>
> 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 <peter.maydell@linaro.org>
> ---
> Guess which exciting new architecture doesn't have getdents :-)
> Tested on i386 by temporarily nobbling the #ifdefs so we use the
> via-getdents64 path rather than via-getdents, and with the test program
> from the getdents(2) manpage as the guest binary.
>
> linux-user/syscall.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 59 insertions(+), 1 deletion(-)
>
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 053fa14..15c771a 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -208,8 +208,11 @@ 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)
> @@ -6963,6 +6966,7 @@ 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;
> @@ -7035,6 +7039,60 @@ 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));

You should use ABI_LONG_ALIGNMENT instead of sizeof(abi_long), as some targets
(at least m68k) don't align on long size.

> +
> + tde->d_ino = tswapal(ino);
> + tde->d_off = tswapal(off);
> + tde->d_reclen = tswap16(treclen);
> + memmove(tde->d_name, de->d_name, namelen + 1);
> + /* 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:

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