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Re: [Qemu-devel] [PATCH v12 3/5] linux-user: Add support for translation
From: |
Laurent Vivier |
Subject: |
Re: [Qemu-devel] [PATCH v12 3/5] linux-user: Add support for translation of statx() syscall |
Date: |
Thu, 27 Jun 2019 16:01:36 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 |
Le 27/06/2019 à 15:18, Aleksandar Markovic a écrit :
>> From: Laurent Vivier <address@hidden>
>>
>>> @@ -10173,6 +10225,88 @@ static abi_long do_syscall1(void *cpu_env, int
>>> num, abi_long > arg1,
>>> ret = host_to_target_stat64(cpu_env, arg3, &st);
>>> return ret;
>>> #endif
>>> +#if defined(TARGET_NR_statx)
>>> + case TARGET_NR_statx:
>>> + {
>>> + struct target_statx *target_stx;
>>> + int dirfd = arg1;
>>> + int flags = arg3;
>>> +
>>> + p = lock_user_string(arg2);
>>> + if (p == NULL) {
>>> + return -TARGET_EFAULT;
>>> + }
>>> +#if defined(__NR_statx)
>>> + {
>>> + /*
>>> + * It is assumed that struct statx is architecture
>>> independent.
>>> + */
>>> + struct target_statx host_stx;
>>> + int mask = arg4;
>>> +
>>> + ret = get_errno(statx(dirfd, p, flags, mask, &host_stx));
>>> + if (!is_error(ret)) {
>>> + if (host_to_target_statx(&host_stx, arg5) != 0) {
>>> + unlock_user(p, arg2, 0);
>>> + return -TARGET_EFAULT;
>>> + }
>>> + }
>>> +
>>> + if (ret != -TARGET_ENOSYS) {
>>> + unlock_user(p, arg2, 0);
>>> + return ret;
>>> + }
>>> + }
>>> +#endif
>>> + if (*((char *)p) == 0) {
>>> + /*
>>> + * By file descriptor
>>> + */
>>> + if (flags & AT_EMPTY_PATH) {
>>> + unlock_user(p, arg2, 0);
>>> + return -TARGET_ENOENT;
>>> + }
>>> + ret = get_errno(fstat(dirfd, &st));
>>> + } else if (*((char *)p) == '/') {
>>> + /*
>>> + * By absolute pathname
>>> + */
>>> + ret = get_errno(stat(path(p), &st));
>>> + } else {
>>> + /*
>>> + * By pathname relative to the current working directory
>>> + * (if 'dirfd' is AT_FDCWD) or relative to the directory
>>> + * referred to by the file descriptor 'dirfd'.
>>> + */
>>> + ret = get_errno(fstatat(dirfd, path(p), &st, flags));
>>> + }
>>> + unlock_user(p, arg2, 0);
>>
>> Could you explain why we can't use fstatat() for the two previous cases
>> "(*((char *)p) == 0)" and "(*((char *)p) == '/')"?
>>
>
> Man page on fstatat (http://man7.org/linux/man-pages/man2/stat.2.html)
> says:
>
> AT_EMPTY_PATH (since Linux 2.6.39)
> If pathname is an empty string, operate on the file referred
> to by dirfd (which may have been obtained using the open(2)
> O_PATH flag). In this case, dirfd can refer to any type of
> file, not just a directory, and the behavior of fstatat() is
> similar to that of fstat(). If dirfd is AT_FDCWD, the call
> operates on the current working directory. This flag is
> Linux-specific; define _GNU_SOURCE to obtain its definition.
>
> So it looks the branch "if (*((char *)p) == 0)" can be handled by
> fstatat().
>
> Also, the man page says:
>
> If pathname is absolute, then dirfd is ignored.
>
> So, it looks the case "else if (*((char *)p) == '/')" can also be
> handled by fstatat().
>
> Very similar descriptions of the cases above can be found in
> the man page for statx
> (http://man7.org/linux/man-pages/man2/statx.2.html).
>
> The whole string of if statements after "#endif" above should be now,
> in my opinion:
>
> ret = get_errno(fstatat(dirfd, path(p), &st, flags));
> unlock_user(p, arg2, 0);
>
> ... and I will submit the patch with such code, if noone objects.
>
I agree.
Thanks,
Laurent
[Qemu-devel] [PATCH v12 4/5] linux-user: Add support for strace for statx() syscall, Aleksandar Markovic, 2019/06/19
Re: [Qemu-devel] [PATCH v12 0/5], no-reply, 2019/06/19
Re: [Qemu-devel] [PATCH v12 0/5], no-reply, 2019/06/19