[pbs-devel] [PATCH proxmox-backup 2/2] tape: changer: sg_pt: correctly loop over MODE SENSE (B8h)

[Dominik Csapak <d.csapak@proxmox.com>]

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>
---
 src/tape/changer/sg_pt_changer.rs | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/src/tape/changer/sg_pt_changer.rs b/src/tape/changer/sg_pt_changer.rs
index 29b04ad6..da114074 100644
--- a/src/tape/changer/sg_pt_changer.rs
+++ b/src/tape/changer/sg_pt_changer.rs
@@ -279,6 +279,7 @@ pub fn transfer_medium<F: AsRawFd>(
 
 fn scsi_read_element_status_cdb(
     start_element_address: u16,
+    number_of_elements: u16,
     allocation_len: u32,
 ) -> Vec<u8> {
 
@@ -287,7 +288,6 @@ fn scsi_read_element_status_cdb(
     cmd.push(1u8<<4); // report all types and volume tags
     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
     cmd.extend(&allocation_len.to_be_bytes()[1..4]);
@@ -315,6 +315,7 @@ pub fn read_element_status<F: AsRawFd>(file: &mut F) -> Result<MtxStatus, Error>
     sg_raw.set_timeout(SCSI_CHANGER_DEFAULT_TIMEOUT);
 
     let mut start_element_address = 0;
+    let number_of_elements: u16 = 1000; // some changers limit the query
 
     let mut drives = Vec::new();
     let mut storage_slots = Vec::new();
@@ -324,12 +325,17 @@ pub fn read_element_status<F: AsRawFd>(file: &mut F) -> Result<MtxStatus, Error>
     let mut retry = true;
 
     loop {
-        let cmd = scsi_read_element_status_cdb(start_element_address, allocation_len);
+        let cmd = scsi_read_element_status_cdb(start_element_address, number_of_elements, 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)?;
 
+        let returned_number_of_elements = page.transports.len()
+            + page.drives.len()
+            + page.storage_slots.len()
+            + page.import_export_slots.len();
+
         retry = false; // only retry the first command
 
         transports.extend(page.transports);
@@ -337,19 +343,16 @@ pub fn read_element_status<F: AsRawFd>(file: &mut F) -> Result<MtxStatus, Error>
         storage_slots.extend(page.storage_slots);
         import_export_slots.extend(page.import_export_slots);
 
-        if data.len() < (allocation_len as usize) {
-            break;
-        }
-
         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 {
+            if last_element_address < start_element_address {
                 bail!("got strange element address");
             }
-        } else {
-            break;
+            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;
     }
 
     if (setup.transport_element_count as usize) != transports.len() {
-- 
2.30.2