[SCSI] Add VPD helper

Based on prior work by Martin Petersen and James Bottomley, this patch
adds a generic helper for retrieving VPD pages from SCSI devices.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

1 files changed, 104 insertions, 0 deletions

diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index cbcd3f681b62..a2ef03243a2c 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -967,6 +967,110 @@ int scsi_track_queue_full(struct scsi_device *sdev, int depth)
 EXPORT_SYMBOL(scsi_track_queue_full);
 
 /**
+ * scsi_vpd_inquiry - Request a device provide us with a VPD page
+ * @sdev: The device to ask
+ * @buffer: Where to put the result
+ * @page: Which Vital Product Data to return
+ * @len: The length of the buffer
+ *
+ * This is an internal helper function.  You probably want to use
+ * scsi_get_vpd_page instead.
+ *
+ * Returns 0 on success or a negative error number.
+ */
+static int scsi_vpd_inquiry(struct scsi_device *sdev, unsigned char *buffer,
+                                                        u8 page, unsigned len)
+{
+        int result;
+        unsigned char cmd[16];
+
+        cmd[0] = INQUIRY;
+        cmd[1] = 1;             /* EVPD */
+        cmd[2] = page;
+        cmd[3] = len >> 8;
+        cmd[4] = len & 0xff;
+        cmd[5] = 0;             /* Control byte */
+
+        /*
+         * I'm not convinced we need to try quite this hard to get VPD, but
+         * all the existing users tried this hard.
+         */
+        result = scsi_execute_req(sdev, cmd, DMA_FROM_DEVICE, buffer,
+                                  len + 4, NULL, 30 * HZ, 3, NULL);
+        if (result)
+                return result;
+
+        /* Sanity check that we got the page back that we asked for */
+        if (buffer[1] != page)
+                return -EIO;
+
+        return 0;
+}
+
+/**
+ * scsi_get_vpd_page - Get Vital Product Data from a SCSI device
+ * @sdev: The device to ask
+ * @page: Which Vital Product Data to return
+ *
+ * SCSI devices may optionally supply Vital Product Data.  Each 'page'
+ * of VPD is defined in the appropriate SCSI document (eg SPC, SBC).
+ * If the device supports this VPD page, this routine returns a pointer
+ * to a buffer containing the data from that page.  The caller is
+ * responsible for calling kfree() on this pointer when it is no longer
+ * needed.  If we cannot retrieve the VPD page this routine returns %NULL.
+ */
+unsigned char *scsi_get_vpd_page(struct scsi_device *sdev, u8 page)
+{
+        int i, result;
+        unsigned int len;
+        unsigned char *buf = kmalloc(259, GFP_KERNEL);
+
+        if (!buf)
+                return NULL;
+
+        /* Ask for all the pages supported by this device */
+        result = scsi_vpd_inquiry(sdev, buf, 0, 255);
+        if (result)
+                goto fail;
+
+        /* If the user actually wanted this page, we can skip the rest */
+        if (page == 0)
+                return buf;
+
+        for (i = 0; i < buf[3]; i++)
+                if (buf[i + 4] == page)
+                        goto found;
+        /* The device claims it doesn't support the requested page */
+        goto fail;
+
+ found:
+        result = scsi_vpd_inquiry(sdev, buf, page, 255);
+        if (result)
+                goto fail;
+
+        /*
+         * Some pages are longer than 255 bytes.  The actual length of
+         * the page is returned in the header.
+         */
+        len = (buf[2] << 8) | buf[3];
+        if (len <= 255)
+                return buf;
+
+        kfree(buf);
+        buf = kmalloc(len + 4, GFP_KERNEL);
+        result = scsi_vpd_inquiry(sdev, buf, page, len);
+        if (result)
+                goto fail;
+
+        return buf;
+
+ fail:
+        kfree(buf);
+        return NULL;
+}
+EXPORT_SYMBOL_GPL(scsi_get_vpd_page);
+
+/**
  * scsi_device_get  -  get an additional reference to a scsi_device
  * @sdev:       device to get a reference to
  *