[v2] ata: libata-scsi: Set the RMB bit only for removable media devices

From: Damien Le Moal <dlemoal@kernel.org>

The SCSI Removable Media Bit (RMB) should only be set for removable media,
where the device stays and the media changes, e.g. CD-ROM or floppy.

The ATA removable media device bit is obsoleted since ATA-8 ACS (2006),
but before that it was used to indicate that the device can have its media
removed (while the device stays).

Commit 8a3e33cf92c7 ("ata: ahci: find eSATA ports and flag them as
removable") introduced a change to set the RMB bit if the port has either
the eSATA bit or the hot-plug capable bit set. The reasoning was that the
author wanted his eSATA ports to get treated like a USB stick.

This is however wrong. See "20-082r23SPC-6: Removable Medium Bit
Expectations" which has since been integrated to SPC, which states that:

"""
Reports have been received that some USB Memory Stick device servers set
the removable medium (RMB) bit to one. The rub comes when the medium is
actually removed, because... The device server is removed concurrently
with the medium removal. If there is no device server, then there is no
device server that is waiting to have removable medium inserted.

Sufficient numbers of SCSI analysts see such a device:
- not as a device that supports removable medium;
but
- as a removable, hot pluggable device.
"""

The definition of the RMB bit in the SPC specification has since been
clarified to match this.

Thus, a USB stick should not have the RMB bit set (and neither shall an
eSATA nor a hot-plug capable port).

Commit dc8b4afc4a04 ("ata: ahci: don't mark HotPlugCapable Ports as
external/removable") then changed so that the RMB bit is only set for the
eSATA bit (and not for the hot-plug capable bit), because of a lot of bug
reports of SATA devices were being automounted by udisks. However,
treating eSATA and hot-plug capable ports differently is not correct.

From the AHCI 1.3.1 spec:
Hot Plug Capable Port (HPCP): When set to '1', indicates that this port's
signal and power connectors are externally accessible via a joint signal
and power connector for blindmate device hot plug.

So a hot-plug capable port is an external port, just like commit
45b96d65ec68 ("ata: ahci: a hotplug capable port is an external port")
claims.

In order to not violate the SPC specification, modify the SCSI INQUIRY
data to only set the RMB bit if the ATA device can have its media removed.

This fixes a reported problem where GNOME/udisks was automounting devices
connected to hot-plug capable ports.

Fixes: 45b96d65ec68 ("ata: ahci: a hotplug capable port is an external port")
Cc: stable@vger.kernel.org
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
Tested-by: Thomas Weißschuh <linux@weissschuh.net>
Reported-by: Thomas Weißschuh <linux@weissschuh.net>
Closes: https://lore.kernel.org/linux-ide/c0de8262-dc4b-4c22-9fac-33432e5bddd3@t-8ch.de/
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
[cassel: wrote commit message]
Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
Changes since v1:
-Added Cc: stable.
-Updated comment and commit message to correctly state that the
 ATA removable media device bit is obsoleted since ATA-8 ACS.

 drivers/ata/libata-scsi.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

On Fri, Jun 14, 2024 at 02:23:45PM +0200, Niklas Cassel wrote:
> From: Damien Le Moal <dlemoal@kernel.org>
> 
> The SCSI Removable Media Bit (RMB) should only be set for removable media,
> where the device stays and the media changes, e.g. CD-ROM or floppy.
> 
> The ATA removable media device bit is obsoleted since ATA-8 ACS (2006),
> but before that it was used to indicate that the device can have its media
> removed (while the device stays).
> 
> Commit 8a3e33cf92c7 ("ata: ahci: find eSATA ports and flag them as
> removable") introduced a change to set the RMB bit if the port has either
> the eSATA bit or the hot-plug capable bit set. The reasoning was that the
> author wanted his eSATA ports to get treated like a USB stick.
> 
> This is however wrong. See "20-082r23SPC-6: Removable Medium Bit
> Expectations" which has since been integrated to SPC, which states that:
> 
> """
> Reports have been received that some USB Memory Stick device servers set
> the removable medium (RMB) bit to one. The rub comes when the medium is
> actually removed, because... The device server is removed concurrently
> with the medium removal. If there is no device server, then there is no
> device server that is waiting to have removable medium inserted.
> 
> Sufficient numbers of SCSI analysts see such a device:
> - not as a device that supports removable medium;
> but
> - as a removable, hot pluggable device.
> """
> 
> The definition of the RMB bit in the SPC specification has since been
> clarified to match this.
> 
> Thus, a USB stick should not have the RMB bit set (and neither shall an
> eSATA nor a hot-plug capable port).
> 
> Commit dc8b4afc4a04 ("ata: ahci: don't mark HotPlugCapable Ports as
> external/removable") then changed so that the RMB bit is only set for the
> eSATA bit (and not for the hot-plug capable bit), because of a lot of bug
> reports of SATA devices were being automounted by udisks. However,
> treating eSATA and hot-plug capable ports differently is not correct.
> 
> From the AHCI 1.3.1 spec:
> Hot Plug Capable Port (HPCP): When set to '1', indicates that this port's
> signal and power connectors are externally accessible via a joint signal
> and power connector for blindmate device hot plug.
> 
> So a hot-plug capable port is an external port, just like commit
> 45b96d65ec68 ("ata: ahci: a hotplug capable port is an external port")
> claims.
> 
> In order to not violate the SPC specification, modify the SCSI INQUIRY
> data to only set the RMB bit if the ATA device can have its media removed.
> 
> This fixes a reported problem where GNOME/udisks was automounting devices
> connected to hot-plug capable ports.
> 
> Fixes: 45b96d65ec68 ("ata: ahci: a hotplug capable port is an external port")
> Cc: stable@vger.kernel.org
> Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
> Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
> Tested-by: Thomas Weißschuh <linux@weissschuh.net>
> Reported-by: Thomas Weißschuh <linux@weissschuh.net>
> Closes: https://lore.kernel.org/linux-ide/c0de8262-dc4b-4c22-9fac-33432e5bddd3@t-8ch.de/
> Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
> [cassel: wrote commit message]
> Signed-off-by: Niklas Cassel <cassel@kernel.org>
> ---
> Changes since v1:
> -Added Cc: stable.
> -Updated comment and commit message to correctly state that the
>  ATA removable media device bit is obsoleted since ATA-8 ACS.
> 
>  drivers/ata/libata-scsi.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> index cdf29b178ddc..bb4d30d377ae 100644
> --- a/drivers/ata/libata-scsi.c
> +++ b/drivers/ata/libata-scsi.c
> @@ -1831,11 +1831,11 @@ static unsigned int ata_scsiop_inq_std(struct ata_scsi_args *args, u8 *rbuf)
>  		2
>  	};
>  
> -	/* set scsi removable (RMB) bit per ata bit, or if the
> -	 * AHCI port says it's external (Hotplug-capable, eSATA).
> +	/*
> +	 * Set the SCSI Removable Media Bit (RMB) if the ATA removable media
> +	 * device bit (obsolete since ATA-8 ACS) is set.
>  	 */
> -	if (ata_id_removable(args->id) ||
> -	    (args->dev->link->ap->pflags & ATA_PFLAG_EXTERNAL))
> +	if (ata_id_removable(args->id))
>  		hdr[1] |= (1 << 7);
>  
>  	if (args->dev->class == ATA_DEV_ZAC) {
> -- 
> 2.45.2
> 

Applied:
https://git.kernel.org/pub/scm/linux/kernel/git/libata/linux.git/log/?h=for-6.10-fixes