Re: [PATCH v4 3/6] util: add Error object for qemu_open_internal error reporting

[Markus Armbruster <armbru@redhat.com>]

Daniel P. Berrangé <berrange@redhat.com> writes:

> Instead of relying on the limited information from errno, we can now
> also provide detailed error messages.

The more detailed error messages are currently always ignored, but the
next patches will fix that.

> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> ---
>  util/osdep.c | 21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/util/osdep.c b/util/osdep.c
> index 9ff92551e7..9c7118d3cb 100644
> --- a/util/osdep.c
> +++ b/util/osdep.c
> @@ -284,7 +284,7 @@ int qemu_lock_fd_test(int fd, int64_t start, int64_t len, bool exclusive)
>   * Opens a file with FD_CLOEXEC set
>   */
>  static int
> -qemu_open_internal(const char *name, int flags, mode_t mode)
> +qemu_open_internal(const char *name, int flags, mode_t mode, Error **errp)
>  {
>      int ret;
>  
> @@ -298,24 +298,31 @@ qemu_open_internal(const char *name, int flags, mode_t mode)
>  
>          fdset_id = qemu_parse_fdset(fdset_id_str);
>          if (fdset_id == -1) {
> +            error_setg(errp, "Could not parse fdset %s", name);
>              errno = EINVAL;
>              return -1;
>          }
>  
>          fd = monitor_fdset_get_fd(fdset_id, flags);
>          if (fd < 0) {
> +            error_setg_errno(errp, -fd, "Could not acquire FD for %s flags %x",
> +                             name, flags);
>              errno = -fd;
>              return -1;
>          }
>  
>          dupfd = qemu_dup_flags(fd, flags);
>          if (dupfd == -1) {
> +            error_setg_errno(errp, errno, "Could not dup FD for %s flags %x",
> +                             name, flags);
>              return -1;
>          }
>  
>          ret = monitor_fdset_dup_fd_add(fdset_id, dupfd);
>          if (ret == -1) {
>              close(dupfd);
> +            error_setg(errp, "Could not save FD for %s flags %x",
> +                       name, flags);

Can this happen?

>              errno = EINVAL;
>              return -1;
>          }
> @@ -336,6 +343,16 @@ qemu_open_internal(const char *name, int flags, mode_t mode)
>      }
>  #endif /* ! O_CLOEXEC */
>  
> +    if (ret == -1) {
> +        const char *action = "open";
> +        if (flags & O_CREAT) {
> +            action = "create";
> +        }
> +        error_setg_errno(errp, errno, "Could not %s '%s' flags 0x%x",
> +                         action, name, flags);

Not a good user experience:

    Could not open '/etc/shadow' flags 0x0: Permission denied

Better:

    Could not open '/etc/shadow' for reading: Permission denied

Are you sure flags other than the access mode (O_RDONLY, O_WRONLY,
O_RDWR) must be included in the error message?

If you must report flags in hexadecimal, then please reporting them more
consistently.  Right now you have

    for %s flags 0x%x
    '%s' flags %x

Perhaps '%s' with flags 0x%x

> +    }
> +
> +
>      return ret;
>  }
>  
> @@ -352,7 +369,7 @@ int qemu_open_old(const char *name, int flags, ...)
>      }
>      va_end(ap);
>  
> -    ret = qemu_open_internal(name, flags, mode);
> +    ret = qemu_open_internal(name, flags, mode, NULL);
>  
>  #ifdef O_DIRECT
>      if (ret == -1 && errno == EINVAL && (flags & O_DIRECT)) {