[PATCH proxmox-backup v2 5/5] fix #7642: avoid expensive user lookups on file locking

[Christian Ebner <c.ebner@proxmox.com>]

Currently each time a backup lock file is being acquired, the backup
user is looked in order to instantiate the create options used if the
lock file is not pre-existing, which requires knowledge of the uid
and gid. backup_user() internally however calls User::from_name(),
which itself uses getpwnam_r(3) [0] and therefore can involve
nsswitch.conf and /etc/passwd parsing, including several syscalls to
do so (see backtrace in linked issue).

Ideally proxmox_product_config::open_api_lockfile() would be used as
drop in replacement for open_backup_lockfile(), which is however not
possible until the currently required legacy locking fallback
implementation remains in place (to be dropped with PBS 5).
Therefore, only switch to
proxmox_product_config::lockfile_create_options() for the time being.
By this the api user as read on init is used for all file lock
operations using this helper.

[0] https://docs.rs/nix/0.29.0/nix/unistd/struct.User.html#method.from_name

Fixes: https://bugzilla.proxmox.com/show_bug.cgi?id=7642
Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
 pbs-config/src/lib.rs | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/pbs-config/src/lib.rs b/pbs-config/src/lib.rs
index b9d5a4d20..73a8a87fa 100644
--- a/pbs-config/src/lib.rs
+++ b/pbs-config/src/lib.rs
@@ -4,6 +4,7 @@ use anyhow::{Error, bail, format_err};
 use hex::FromHex;
 use nix::unistd::{Gid, Group, Uid, User};
 
+use proxmox_product_config::lockfile_create_options;
 use proxmox_sys::fs::DirLockGuard;
 
 pub use pbs_buildcfg::{BACKUP_GROUP_NAME, BACKUP_USER_NAME};
@@ -106,11 +107,9 @@ pub fn open_backup_lockfile<P: AsRef<std::path::Path>>(
     timeout: Option<std::time::Duration>,
     exclusive: bool,
 ) -> Result<BackupLockGuard, Error> {
-    let user = backup_user()?;
-    let options = proxmox_sys::fs::CreateOptions::new()
-        .perm(nix::sys::stat::Mode::from_bits_truncate(0o660))
-        .owner(user.uid)
-        .group(user.gid);
+    // TODO: Replace whole helper with proxmox_product_config::open_api_lockfile() when
+    // dropping _legacy_dir in in PBS5.
+    let options = lockfile_create_options();
 
     let timeout = timeout.unwrap_or(std::time::Duration::new(10, 0));
 
-- 
2.47.3