tape: changer: sg_pt: query element types separately

Some changers do not like the DVCID bit when querying non-drives,
this includes when querying 'all' elements.

To circumvent this, we query each type by itself (like mtx does it),
and only add the DVCID bit for drives (Data Transfer Elements).

Reported by a user in the forum:
https://forum.proxmox.com/threads/ibm-3584-ts3500-support.92291/

and limit to 1000 elements per request.
(Because some changers limit that request with the options we set)

instead of checking if the data len was equal to the allocation_len
for getting more data, we count the returned elements and compare
that with the number we requested

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
Signed-off-by: Dietmar Maurer <dietmar@proxmox.com>

src/tape/changer/sg_pt_changer.rs

@@ -278,19 +278,33 @@ pub fn transfer_medium<F: AsRawFd>(
     Ok(())
 }
 
+#[repr(u8)]
+#[derive(Clone, Copy)]
+enum ElementType {
+    MediumTransport = 1,
+    Storage = 2,
+    ImportExport = 3,
+    DataTransfer = 4,
+}
+
 fn scsi_read_element_status_cdb(
     start_element_address: u16,
+    number_of_elements: u16,
+    element_type: ElementType,
     allocation_len: u32,
 ) -> Vec<u8> {
 
     let mut cmd = Vec::new();
     cmd.push(0xB8); // READ ELEMENT STATUS (B8h)
-    cmd.push(1u8<<4); // report all types and volume tags
+    cmd.push(1u8<<4 | (element_type as u8)); // volume tags and given type
     cmd.extend(&start_element_address.to_be_bytes());
 
-    let number_of_elements: u16 = 0xffff;
     cmd.extend(&number_of_elements.to_be_bytes());
-    cmd.push(0b001); //  Mixed=0,CurData=0,DVCID=1
+    let byte6 = match element_type {
+        ElementType::DataTransfer => 0b001, //  Mixed=0,CurData=0,DVCID=1
+        _ => 0b000, // Mixed=0,CurData=0,DVCID=0
+    };
+    cmd.push(byte6);
     cmd.extend(&allocation_len.to_be_bytes()[1..4]);
     cmd.push(0);
     cmd.push(0);
@@ -298,6 +312,61 @@ fn scsi_read_element_status_cdb(
     cmd
 }
 
+// query a single element type from the changer
+fn get_element<F: AsRawFd>(
+    inquiry: &InquiryInfo,
+    sg_raw: &mut SgRaw<F>,
+    element_type: ElementType,
+    allocation_len: u32,
+    mut retry: bool,
+) -> Result<DecodedStatusPage, Error> {
+
+    let mut start_element_address = 0;
+    let number_of_elements: u16 = 1000; // some changers limit the query
+
+    let mut result = DecodedStatusPage {
+        last_element_address: None,
+        transports: Vec::new(),
+        drives: Vec::new(),
+        storage_slots: Vec::new(),
+        import_export_slots: Vec::new(),
+    };
+
+    loop {
+        let cmd = scsi_read_element_status_cdb(start_element_address, number_of_elements, element_type, allocation_len);
+
+        let data = execute_scsi_command(sg_raw, &cmd, "read element status (B8h)", retry)?;
+
+        let page = decode_element_status_page(&inquiry, &data, start_element_address)?;
+
+        retry = false; // only retry the first command
+
+        let returned_number_of_elements = page.transports.len()
+            + page.drives.len()
+            + page.storage_slots.len()
+            + page.import_export_slots.len();
+
+        result.transports.extend(page.transports);
+        result.drives.extend(page.drives);
+        result.storage_slots.extend(page.storage_slots);
+        result.import_export_slots.extend(page.import_export_slots);
+        result.last_element_address = page.last_element_address;
+
+        if let Some(last_element_address) = page.last_element_address {
+            if last_element_address < start_element_address {
+                bail!("got strange element address");
+            }
+            if returned_number_of_elements >= (number_of_elements as usize) {
+                start_element_address = last_element_address + 1;
+                continue; // we possibly have to read additional elements
+            }
+        }
+        break;
+    }
+
+    Ok(result)
+}
+
 /// Read element status.
 pub fn read_element_status<F: AsRawFd>(file: &mut F) -> Result<MtxStatus, Error> {
 
@@ -315,43 +384,22 @@ pub fn read_element_status<F: AsRawFd>(file: &mut F) -> Result<MtxStatus, Error>
     let mut sg_raw = SgRaw::new(file, allocation_len as usize)?;
     sg_raw.set_timeout(SCSI_CHANGER_DEFAULT_TIMEOUT);
 
-    let mut start_element_address = 0;
-
     let mut drives = Vec::new();
     let mut storage_slots = Vec::new();
     let mut import_export_slots = Vec::new();
     let mut transports = Vec::new();
 
-    let mut retry = true;
-
-    loop {
-        let cmd = scsi_read_element_status_cdb(start_element_address, allocation_len);
-
-        let data = execute_scsi_command(&mut sg_raw, &cmd, "read element status (B8h)", retry)?;
-
-        let page = decode_element_status_page(&inquiry, &data, start_element_address)?;
-
-        retry = false; // only retry the first command
-
-        transports.extend(page.transports);
-        drives.extend(page.drives);
+    let page = get_element(&inquiry, &mut sg_raw, ElementType::Storage, allocation_len, true)?;
     storage_slots.extend(page.storage_slots);
+
+    let page = get_element(&inquiry, &mut sg_raw, ElementType::ImportExport, allocation_len, false)?;
     import_export_slots.extend(page.import_export_slots);
 
-        if data.len() < (allocation_len as usize) {
-            break;
-        }
+    let page = get_element(&inquiry, &mut sg_raw, ElementType::DataTransfer, allocation_len, false)?;
+    drives.extend(page.drives);
 
-        if let Some(last_element_address) = page.last_element_address {
-            if last_element_address >= start_element_address {
-                start_element_address = last_element_address + 1;
-            } else {
-                bail!("got strange element address");
-            }
-        } else {
-            break;
-        }
-    }
+    let page = get_element(&inquiry, &mut sg_raw, ElementType::MediumTransport, allocation_len, false)?;
+    transports.extend(page.transports);
 
     if (setup.transport_element_count as usize) != transports.len() {
         bail!("got wrong number of transport elements");