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

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

[Dominik Csapak]

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

[pbs-devel] [PATCH proxmox-backup v4 2/2] tape: changer: improve error message on wrong counts

[Dominik Csapak]

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
---
 src/tape/changer/sg_pt_changer.rs | 37 ++++++++++++++++++++++++-------
 1 file changed, 29 insertions(+), 8 deletions(-)

diff --git a/src/tape/changer/sg_pt_changer.rs b/src/tape/changer/sg_pt_changer.rs
index 098c10d8..daa1ad82 100644
--- a/src/tape/changer/sg_pt_changer.rs
+++ b/src/tape/changer/sg_pt_changer.rs
@@ -421,17 +421,38 @@ pub fn read_element_status<F: AsRawFd>(file: &mut F) -> Result<MtxStatus, Error>
     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");
+    let transport_count = setup.transport_element_count as usize;
+    let storage_count = setup.storage_element_count as usize;
+    let import_export_count = setup.import_export_element_count as usize;
+    let transfer_count = setup.transfer_element_count as usize;
+
+    if transport_count != transports.len() {
+        bail!(
+            "got wrong number of transport elements: expoected {}, got{}",
+            transport_count,
+            transports.len()
+        );
     }
-    if (setup.storage_element_count as usize) != storage_slots.len() {
-        bail!("got wrong number of storage elements");
+    if storage_count != storage_slots.len() {
+        bail!(
+            "got wrong number of storage elements: expected {}, got {}",
+            storage_count,
+            storage_slots.len(),
+        );
     }
-    if (setup.import_export_element_count as usize) != import_export_slots.len() {
-        bail!("got wrong number of import/export elements");
+    if import_export_count != import_export_slots.len() {
+        bail!(
+            "got wrong number of import/export elements: expected {}, got {}",
+            import_export_count,
+            import_export_slots.len(),
+        );
     }
-    if (setup.transfer_element_count as usize) != drives.len() {
-        bail!("got wrong number of transfer elements");
+    if transfer_count != drives.len() {
+        bail!(
+            "got wrong number of transfer elements: expected {}, got {}",
+            transfer_count,
+            drives.len(),
+        );
     }
 
     // create same virtual slot order as mtx(1)
-- 
2.30.2

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

[Dietmar Maurer]

applied both patches

On 7/22/21 11:26 AM, Dominik Csapak wrote:
> 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)?;
> -                }
>               }
>           }
>