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From: Gabriel Goller <g.goller@proxmox.com>
To: pbs-devel@lists.proxmox.com
Date: Wed, 15 Nov 2023 12:01:03 +0100
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Subject: [pbs-devel] [PATCH proxmox] sys: open process_locker lockfile lazy
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When setting a datastore in maintenance mode (offline or read-only) we
should be able to unmount it. This isn't possible because the
`ChunkReader` has a `ProcessLocker` instance that holds an open
file descriptor to (f.e.) `/mnt/datastore/test1/.lock`.
The `ChunkReader` is created at startup, so if the datastore is not set
to a maintenance mode at startup, we always have the lockfile open.
Now we create/open the lockfile lazy, when a shared lock or a exclusive
lock is wanted. Like this, we can set a datastore to 'offline' and
unmount it without restarting the proxmox-backup service.
Signed-off-by: Gabriel Goller <g.goller@proxmox.com>
---
proxmox-sys/src/process_locker.rs | 79 +++++++++++++++++++++++--------
1 file changed, 58 insertions(+), 21 deletions(-)
diff --git a/proxmox-sys/src/process_locker.rs b/proxmox-sys/src/process_locker.rs
index 4874da8..b612317 100644
--- a/proxmox-sys/src/process_locker.rs
+++ b/proxmox-sys/src/process_locker.rs
@@ -8,7 +8,9 @@
//! `oldest_shared_lock()`.
use std::collections::HashMap;
+use std::fs::File;
use std::os::unix::io::AsRawFd;
+use std::path::PathBuf;
use std::sync::{Arc, Mutex};
use anyhow::{bail, Error};
@@ -19,7 +21,8 @@ use anyhow::{bail, Error};
/// Inter-process reader-writer lock
pub struct ProcessLocker {
- file: std::fs::File,
+ path: PathBuf,
+ file_descriptor: Option<File>,
exclusive: bool,
writers: usize,
next_guard_id: u64,
@@ -53,11 +56,16 @@ impl Drop for ProcessLockSharedGuard {
l_pid: 0,
};
- if let Err(err) =
- nix::fcntl::fcntl(data.file.as_raw_fd(), nix::fcntl::FcntlArg::F_SETLKW(&op))
- {
- panic!("unable to drop writer lock - {}", err);
+ if let Some(file) = &data.file_descriptor {
+ if let Err(err) =
+ nix::fcntl::fcntl(file.as_raw_fd(), nix::fcntl::FcntlArg::F_SETLKW(&op))
+ {
+ panic!("unable to drop writer lock - {}", err);
+ }
+ } else {
+ panic!("file descriptor has been closed while locking");
}
+ data.file_descriptor = None;
}
if data.writers > 0 {
data.writers -= 1;
@@ -93,29 +101,31 @@ impl Drop for ProcessLockExclusiveGuard {
l_pid: 0,
};
- if let Err(err) =
- nix::fcntl::fcntl(data.file.as_raw_fd(), nix::fcntl::FcntlArg::F_SETLKW(&op))
- {
- panic!("unable to drop exclusive lock - {}", err);
+ if let Some(file) = &data.file_descriptor {
+ if let Err(err) =
+ nix::fcntl::fcntl(file.as_raw_fd(), nix::fcntl::FcntlArg::F_SETLKW(&op))
+ {
+ panic!("unable to drop exclusive lock - {}", err);
+ }
+ } else {
+ panic!("file descriptor has been closed while locking");
}
+ println!("closing exclusive file lock");
+ data.file_descriptor = None;
data.exclusive = false;
}
}
impl ProcessLocker {
- /// Create a new instance for the specified file.
+ /// Create a new instance of the ProcessLocker.
///
- /// This simply creates the file if it does not exist.
- pub fn new<P: AsRef<std::path::Path>>(lockfile: P) -> Result<Arc<Mutex<Self>>, Error> {
- let file = std::fs::OpenOptions::new()
- .create(true)
- .read(true)
- .write(true)
- .open(lockfile)?;
-
+ /// Does not check if the lockfile exists. The lockfile gets opened/created
+ /// when using [Self::try_shared_lock()] or [Self::try_exclusive_lock()].
+ pub fn new(lockfile: PathBuf) -> Result<Arc<Mutex<Self>>, Error> {
Ok(Arc::new(Mutex::new(Self {
- file,
+ path: lockfile,
+ file_descriptor: None,
exclusive: false,
writers: 0,
next_guard_id: 0,
@@ -144,7 +154,20 @@ impl ProcessLocker {
let mut data = locker.lock().unwrap();
if data.writers == 0 && !data.exclusive {
- if let Err(err) = Self::try_lock(&data.file, libc::F_RDLCK) {
+ if data.file_descriptor.is_none() {
+ let file = std::fs::OpenOptions::new()
+ .create(true)
+ .read(true)
+ .write(true)
+ .open(&data.path)?;
+ data.file_descriptor = Some(file);
+ }
+ if let Err(err) = Self::try_lock(
+ data.file_descriptor
+ .as_ref()
+ .expect("unable to open lockfile"),
+ libc::F_RDLCK,
+ ) {
bail!("unable to get shared lock - {}", err);
}
}
@@ -187,7 +210,21 @@ impl ProcessLocker {
bail!("already locked exclusively");
}
- if let Err(err) = Self::try_lock(&data.file, libc::F_WRLCK) {
+ if data.file_descriptor.is_none() {
+ let file = std::fs::OpenOptions::new()
+ .create(true)
+ .read(true)
+ .write(true)
+ .open(&data.path)?;
+ data.file_descriptor = Some(file);
+ }
+ println!("locking exclusive lock: {:?}", &data.file_descriptor);
+ if let Err(err) = Self::try_lock(
+ data.file_descriptor
+ .as_ref()
+ .expect("unable to open lockfile"),
+ libc::F_WRLCK,
+ ) {
bail!("unable to get exclusive lock - {}", err);
}
--
2.39.2