Re: [PATCH] ata: implement MODE SELECT command

Sergei Shtylyov
2012-07-04T15:40:06Z

Hello.

On 07/04/2012 03:13 PM, Paolo Bonzini wrote:

> The cache_type file in sysfs lets users configure the disk cache in
> write-through or write-back modes. However, ata disks do not support
> writing to the file because they do not implement the MODE SELECT
> command.

> This patch adds a translation from MODE SELECT (for the caching page
> only) to the ATA SET FEATURES command.

> Cc: Jeff Garzik <jgarzik@pobox.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> drivers/ata/libata-scsi.c | 147 +++++++++++++++++++++++++++++++++++++++++++--
> 1 files changed, 142 insertions(+), 5 deletions(-)

> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> index 41cde45..e7702d3 100644
> --- a/drivers/ata/libata-scsi.c
> +++ b/drivers/ata/libata-scsi.c
> @@ -3081,6 +3081,144 @@ static unsigned int ata_scsi_write_same_xlat(struct ata_queued_cmd *qc)
> }
>
> /**
> + * ata_mselect_caching - Simulate MODE SELECT for caching info page
> + * @tf: taskfile to be filled
> + * @buf: input buffer
> + * @len: number of valid bytes in the input buffer
> + *
> + * Prepare a taskfile to modify caching information for the device.
> + *
> + * LOCKING:
> + * None.
> + */
> +static unsigned int ata_mselect_caching(struct ata_taskfile *tf, const u8 *buf,
> + int len)
> +{
> + u8 wce;

Empty line after declaration block wouldn't hurt...

> + if (len == 0)
> + return 1;
> +
> + /*
> + * The first two bytes are a header, so offsets here are 2 less
> + * than in ata_msense_caching.
> + */
> + wce = buf[0] & (1 << 2);

Perhaps it's worth denying the command if the other page fields dfifer from
'def_cache_mpage' (i.e. all zeros)?

> +/**
> + * ata_scsi_mode_select_xlat - Translate MODE SELECT 6, 10 commands
> + * @qc: Storage for translated ATA taskfile
> + *
> + * Converts a MODE SELECT command to an ATA SET FEATURES taskfile.
> + * Assume this is invoked for direct access devices (e.g. disks) only.
> + * There should be no block descriptor for other device types.
> + *
> + * LOCKING:
> + * spin_lock_irqsave(host lock)
> + */
> +static unsigned int ata_scsi_mode_select_xlat(struct ata_queued_cmd *qc)
> +{
> + struct scsi_cmnd *scmd = qc->scsicmd;
> + struct ata_taskfile *tf = &qc->tf;
> + const u8 *cdb = scmd->cmnd;
> + const u8 *p;
> + u8 pg, spg;
> + unsigned six_byte, pg_len;
> + int len;
> +
> + VPRINTK("ENTER\n");
> +
> + /*
> + * Get the command buffer.
> + */
> + if (!scsi_sg_count(scmd))
> + goto invalid_fld;
> +
> + p = page_address(sg_page(scsi_sglist(scmd)));
> +
> + six_byte = (cdb[0] == MODE_SELECT);
> + if (six_byte) {
> + if (scmd->cmd_len < 5)

Not 6?

> + goto invalid_fld;
> +
> + len = cdb[4];
> + } else {
> + if (scmd->cmd_len < 9)

Not 10?
And ata_scsiop_mode_sense() don't seem to check this...
And I doubt "Invalid field in CDB" is a proper sense code in this situation.

> + goto invalid_fld;
> +
> + len = (cdb[7] << 8) | cdb[8];
> + }

> + /*
> + * No mode subpages supported (yet) but asking for _all_
> + * subpages may be valid
> + */
> + if (spg && (spg != ALL_SUB_MPAGES))
> + goto invalid_fld;
> + if (pg_len > len)
> + goto invalid_fld;

It's valid to have buffer size less than data size.

> + switch (pg) {
> + case CACHE_MPAGE:
> + if (ata_mselect_caching(tf, p, pg_len))
> + goto invalid_fld;
> + break;
> +
> + default: /* invalid page code */
> + goto invalid_fld;

Page code is not a part of CDB, hence the sense code you'll return doesn't
fit there.

> + }
> + return 0;
> +
> + invalid_fld:
> + ata_scsi_set_sense(scmd, ILLEGAL_REQUEST, 0x24, 0x0);
> + /* "Invalid field in cbd" */
> + return 1;

MBR, Sergei