[pbs-devel] [PATCH proxmox-backup v4 1/2] tape: changer: correctly consume data in decode_element_status_page

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

instead of 'blindly' trusting the changer to deliver the fields written
in the specification, trust the length data it returns in the header.

we slice the descriptor data into equal sized chunks of the correct
size, then we do not have care bout the len and empty checks anymore

this also makes the code to read the rest of the page obsolete,
since the next descriptor is on the correct offset anyway

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
---
 src/tape/changer/sg_pt_changer.rs | 31 ++-----------------------------
 1 file changed, 2 insertions(+), 29 deletions(-)

diff --git a/src/tape/changer/sg_pt_changer.rs b/src/tape/changer/sg_pt_changer.rs
index a15d8192..098c10d8 100644
--- a/src/tape/changer/sg_pt_changer.rs
+++ b/src/tape/changer/sg_pt_changer.rs
@@ -651,17 +651,9 @@ fn decode_element_status_page(
             }
 
             let descr_data = reader.read_exact_allocated(len)?;
-            let mut reader = &descr_data[..];
 
-            loop {
-                if reader.is_empty() {
-                    break;
-                }
-                if reader.len() < (subhead.descriptor_length as usize) {
-                    break;
-                }
-
-                let len_before = reader.len();
+            for descriptor in descr_data.chunks_exact(subhead.descriptor_length as usize) {
+                let mut reader = &descriptor[..];
 
                 match subhead.element_type_code {
                     1 => {
@@ -672,9 +664,6 @@ fn decode_element_status_page(
 
                         subhead.skip_alternate_volume_tag(&mut reader)?;
 
-                        let mut reserved = [0u8; 4];
-                        reader.read_exact(&mut reserved)?;
-
                         result.last_element_address = Some(desc.element_address);
 
                         let status = TransportElementStatus {
@@ -691,9 +680,6 @@ fn decode_element_status_page(
 
                         subhead.skip_alternate_volume_tag(&mut reader)?;
 
-                        let mut reserved = [0u8; 4];
-                        reader.read_exact(&mut reserved)?;
-
                         result.last_element_address = Some(desc.element_address);
 
                         if subhead.element_type_code == 3 {
@@ -763,19 +749,6 @@ fn decode_element_status_page(
                     }
                     code => bail!("got unknown element type code {}", code),
                 }
-
-                // we have to consume the whole descriptor size, else
-                // our position in the reader is not correct
-                let len_after = reader.len();
-                let have_read = len_before - len_after;
-                let desc_len = subhead.descriptor_length as usize;
-                if desc_len > have_read {
-                    let mut left_to_read = desc_len - have_read;
-                    if left_to_read > len_after {
-                        left_to_read = len_after; // reader has not enough data?
-                    }
-                    let _ = reader.read_exact_allocated(left_to_read)?;
-                }
             }
         }
 
-- 
2.30.2