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

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Aug 25, 2020 at 05:14:21PM +0200, Markus Armbruster wrote:
> 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?

Well there's code in monitor_fdset_dup_fd_add that can return -1.

> 
> >              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?

It was the flags other than access mode that I was thinking were
more important to log. I'm ambivalent htough, so can drop the
flags if it is thought to be overkill.

> 
> 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)) {
> 
> 

Regards,
Daniel
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