Re: [Qemu-devel] [PATCH v4 5/5] atapi: GESN: implement 'media' subcommand

[Amit Shah <amit.shah@redhat.com>]

On (Tue) 12 Apr 2011 [17:11:22], Kevin Wolf wrote:
> Am 12.04.2011 17:03, schrieb Amit Shah:
> > On (Tue) 12 Apr 2011 [16:54:53], Kevin Wolf wrote:
> >> Am 12.04.2011 16:09, schrieb Amit Shah:
> >>> Implement the 'media' sub-command of the GET_EVENT_STATUS_NOTIFICATION
> >>> command.  This helps us report tray open, tray closed, no media, media
> >>> present states to the guest.
> >>>
> >>> Newer Linux kernels (2.6.38+) rely on this command to revalidate discs
> >>> after media change.
> >>>
> >>> This patch also sends out tray open/closed status to the guest driver
> >>> when requested e.g. via the CDROM_DRIVE_STATUS ioctl (thanks Markus).
> >>> Without such notification, the guest and qemu's tray open/close status
> >>> was frequently out of sync, causing installers like Anaconda detecting
> >>> no disc instead of tray open, confusing them terribly.
> >>>
> >>> Signed-off-by: Amit Shah <amit.shah@redhat.com>
> >>> ---
> >>>  hw/ide/core.c     |  109 ++++++++++++++++++++++++++++++++++++++++++++++++++--
> >>>  hw/ide/internal.h |    6 +++
> >>>  2 files changed, 110 insertions(+), 5 deletions(-)
> >>>
> >>> diff --git a/hw/ide/core.c b/hw/ide/core.c
> >>> index dafc049..209d8e6 100644
> >>> --- a/hw/ide/core.c
> >>> +++ b/hw/ide/core.c
> >>> @@ -1084,6 +1084,49 @@ static int ide_dvd_read_structure(IDEState *s, int format,
> >>>      }
> >>>  }
> >>>  
> >>> +static unsigned int event_status_media(IDEState *s,
> >>> +                                       uint8_t *buf,
> >>> +                                       unsigned int max_len)
> >>> +{
> >>> +    enum media_event_code {
> >>> +        no_change = 0,       /* Status unchanged */
> >>> +        eject_requested,     /* received a request from user to eject */
> >>> +        new_media,           /* new media inserted and ready for access */
> >>> +        media_removal,       /* only for media changers */
> >>> +        media_changed,       /* only for media changers */
> >>> +        bg_format_completed, /* MRW or DVD+RW b/g format completed */
> >>> +        bg_format_restarted, /* MRW or DVD+RW b/g format restarted */
> >>> +    };
> >>> +    enum media_status {
> >>> +        tray_open = 1,
> >>> +        media_present = 2,
> >>> +    };
> >>> +    uint8_t event_code, media_status;
> >>> +
> >>> +    media_status = 0;
> >>> +    if (s->bs->tray_open) {
> >>> +        media_status = tray_open;
> >>> +    } else if (bdrv_is_inserted(s->bs)) {
> >>> +        media_status = media_present;
> >>> +    }
> >>> +
> >>> +    /* Event notification descriptor */
> >>> +    event_code = no_change;
> >>> +    if (media_status != tray_open && s->events.new_media) {
> >>> +        event_code = new_media;
> >>> +        s->events.new_media = false;
> >>> +    }
> >>> +
> >>> +    buf[4] = event_code;
> >>> +    buf[5] = media_status;
> >>> +
> >>> +    /* These fields are reserved, just clear them. */
> >>> +    buf[6] = 0;
> >>> +    buf[7] = 0;
> >>> +
> >>> +    return 8; /* We wrote to 4 extra bytes from the header */
> >>> +}
> >>> +
> >>>  static void handle_get_event_status_notification(IDEState *s,
> >>>                                                   uint8_t *buf,
> >>>                                                   const uint8_t *packet)
> >>> @@ -1104,6 +1147,26 @@ static void handle_get_event_status_notification(IDEState *s,
> >>>          uint8_t supported_events;
> >>>      } __attribute((packed)) *gesn_event_header;
> >>>  
> >>> +    enum notification_class_request_type {
> >>> +        reserved1 = 1 << 0,
> >>> +        operational_change = 1 << 1,
> >>> +        power_management = 1 << 2,
> >>> +        external_request = 1 << 3,
> >>> +        media = 1 << 4,
> >>> +        multi_host = 1 << 5,
> >>> +        device_busy = 1 << 6,
> >>> +        reserved2 = 1 << 7,
> >>> +    };
> >>> +    enum event_notification_class_field {
> >>> +        enc_no_events = 0,
> >>> +        enc_operational_change,
> >>> +        enc_power_management,
> >>> +        enc_external_request,
> >>> +        enc_media,
> >>> +        enc_multiple_hosts,
> >>> +        enc_device_busy,
> >>> +        enc_reserved,
> >>> +    };
> >>>      unsigned int max_len, used_len;
> >>>  
> >>>      gesn_cdb = (void *)packet;
> >>> @@ -1121,12 +1184,25 @@ static void handle_get_event_status_notification(IDEState *s,
> >>>  
> >>>      /* polling mode operation */
> >>>  
> >>> -    /* We don't support any event class (yet). */
> >>> -    gesn_event_header->supported_events = 0;
> >>> -
> >>> -    gesn_event_header->notification_class = 0x80; /* No event available */
> >>> -    used_len = sizeof(*gesn_event_header);
> >>> +    /*
> >>> +     * These are the supported events.
> >>> +     *
> >>> +     * We currently only support requests of the 'media' type.
> >>> +     */
> >>> +    gesn_event_header->supported_events = media;
> >>>  
> >>> +    /*
> >>> +     * Responses to requests are to be based on request priority.  The
> >>> +     * notification_class_request_type enum above specifies the
> >>> +     * priority: upper elements are higher prio than lower ones.
> >>> +     */
> >>> +    if (gesn_cdb->class & media) {
> >>> +        gesn_event_header->notification_class |= enc_media;
> >>
> >> Am I missing where this field is initialized or should it be = instead
> >> of |= ?
> > 
> > I considered both: if the 'reserved' bits become available and if we
> > should write to them, |= makes more sense.  Currently, = will
> > suffice.  Strong preference?
> 
> |= is fine if the field is initialized to 0 and you add flags to it. But
> this patch seems to remove the zero initialization. Maybe it's still
> there somewhere, I just don't see it right now.

Yes, I didn't think about it when you asked to remove the 0 init, but
got reminded after I saw this comment.  I'll do a v5 with the init
back in.

		Amit