[PATCH v1 proxmox-backup 11/11] tape: media catalog: use Flock wrapper instead of deprecated function

[Robert Obkircher <r.obkircher@proxmox.com>]

Switch to the new wrapper type to fix the deprecation warnings. Panic
if unlock fails, because there is no easy way to return the File that
was temporarily moved out of the field.

An alternative to moving out of the optional field would be to use
`File::try_clone` but that isn't ideal either because duplicated file
descriptors share the same lock status. That also doesn't solve the
problem that propagating the error without leaking the locked file
descriptor requires unsafe code or a change to nix.

[1] https://lore.proxmox.com/pbs-devel/1763634535.5sqd1r4buu.astroid@yuna.none/

Signed-off-by: Robert Obkircher <r.obkircher@proxmox.com>
---
 src/tape/media_catalog.rs | 49 +++++++++++++++++++++------------------
 1 file changed, 27 insertions(+), 22 deletions(-)

diff --git a/src/tape/media_catalog.rs b/src/tape/media_catalog.rs
index 63329a65..372bf59d 100644
--- a/src/tape/media_catalog.rs
+++ b/src/tape/media_catalog.rs
@@ -6,6 +6,7 @@ use std::path::{Path, PathBuf};
 
 use anyhow::{bail, format_err, Error};
 use endian_trait::Endian;
+use nix::fcntl::{Flock, FlockArg};
 
 use proxmox_sys::fs::read_subdir;
 
@@ -194,7 +195,7 @@ impl MediaCatalog {
         let me = proxmox_lang::try_block!({
             Self::create_basedir(base_path)?;
 
-            let mut file = std::fs::OpenOptions::new()
+            let file = std::fs::OpenOptions::new()
                 .read(true)
                 .write(write)
                 .create(create)
@@ -219,9 +220,10 @@ impl MediaCatalog {
             };
 
             // Note: lock file, to get a consistent view with load_catalog
-            nix::fcntl::flock(file.as_raw_fd(), nix::fcntl::FlockArg::LockExclusive)?;
+            let mut file = Flock::lock(file, FlockArg::LockExclusive)
+                .map_err(|e| format_err!("flock failed: {e:?}"))?;
             let result = me.load_catalog(&mut file, media_id.media_set_label.as_ref());
-            nix::fcntl::flock(file.as_raw_fd(), nix::fcntl::FlockArg::Unlock)?;
+            let file = file.unlock().expect("shouldn't fail for valid fd");
 
             let (found_magic_number, _) = result?;
 
@@ -367,27 +369,30 @@ impl MediaCatalog {
             return Ok(());
         }
 
-        match self.file {
-            Some(ref mut file) => {
-                let pending = &self.pending;
-                // Note: lock file, to get a consistent view with load_catalog
-                nix::fcntl::flock(file.as_raw_fd(), nix::fcntl::FlockArg::LockExclusive)?;
-                let result: Result<(), Error> = proxmox_lang::try_block!({
-                    file.write_all(pending)?;
-                    file.flush()?;
-                    file.sync_data()?;
-                    Ok(())
-                });
-                nix::fcntl::flock(file.as_raw_fd(), nix::fcntl::FlockArg::Unlock)?;
-
-                result?;
-            }
-            None => bail!("media catalog not writable (opened read only)"),
-        }
+        let Some(file) = self.file.take() else {
+            bail!("media catalog not writable (opened read only)");
+        };
+
+        let mut file = Flock::lock(file, FlockArg::LockExclusive).map_err(|(f, e)| {
+            self.file = Some(f);
+            format_err!("flock failed: {:?} - {e:?}", self.file)
+        })?;
 
-        self.pending = Vec::new();
+        let pending = &self.pending;
+        // Note: lock file, to get a consistent view with load_catalog
+        let result: Result<(), Error> = proxmox_lang::try_block!({
+            file.write_all(pending)?;
+            file.flush()?;
+            file.sync_data()?;
+            Ok(())
+        });
 
-        Ok(())
+        self.file = Some(file.unlock().expect("shouldn't fail for valid fd"));
+
+        if result.is_ok() {
+            self.pending = Vec::new();
+        }
+        result
     }
 
     /// Conditionally commit if in pending data is large (> 1Mb)
-- 
2.47.3