[pbs-devel] [PATCH proxmox-backup] tape: work around buggy changer implementations

[pbs-devel] [PATCH proxmox-backup] tape: work around buggy changer implementations

[Dominik Csapak]

allocation length for read element status is a 3 byte field, but it
seems some changers only look at the bottom two bytes. Since we used
0x010000 for it, those changers did not return any data and the calls
failed.

To work around it, request one byte less (0xFFFF) which should still be
enough for the data, but should now work with those buggy
implementations.

Reported by a user in the forum: https://forum.proxmox.com/threads/137391/

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
---
 pbs-tape/src/sg_pt_changer.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pbs-tape/src/sg_pt_changer.rs b/pbs-tape/src/sg_pt_changer.rs
index cfddbf9a..c82bd8f6 100644
--- a/pbs-tape/src/sg_pt_changer.rs
+++ b/pbs-tape/src/sg_pt_changer.rs
@@ -369,7 +369,7 @@ pub fn read_element_status<F: AsRawFd>(file: &mut F) -> Result<MtxStatus, Error>
     // first, request address assignment (used for sanity checks)
     let setup = read_element_address_assignment(file)?;
 
-    let allocation_len: u32 = 0x10000;
+    let allocation_len: u32 = 0xFFFF;
 
     let mut sg_raw = SgRaw::new(file, allocation_len as usize)?;
     sg_raw.set_timeout(SCSI_CHANGER_DEFAULT_TIMEOUT);
-- 
2.30.2

Re: [pbs-devel] [PATCH proxmox-backup] tape: work around buggy changer implementations

[Dietmar Maurer]

Please add an comment here, to make sure that we do not change it back later.

> -    let allocation_len: u32 = 0x10000;
> +    let allocation_len: u32 = 0xFFFF;