[pbs-devel] [PATCH v6 proxmox-backup 62/65] client: tools: add helper to raise nofile rlimit

[Christian Ebner]

The default soft limit for open file handles is rather low, as some
apis (e.g. the POSIX `select(2)` syscall) do not work [0].

The lookahead cache use during the backup clients metadata comparison
to reuse unchanged files however requires much higher limits to work
effectively.

This helper function allows to raise the soft limit to the hard
limit, as provided by the `getrlimit(2)` syscall.

[0] https://0pointer.net/blog/file-descriptor-limits.html

Suggested-by: Thomas Lamprecht <t.lamprecht at proxmox.com>
Signed-off-by: Christian Ebner <c.ebner at proxmox.com>
---
 pbs-client/src/tools/mod.rs | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/pbs-client/src/tools/mod.rs b/pbs-client/src/tools/mod.rs
index e6cf066e4..8de8b6b80 100644
--- a/pbs-client/src/tools/mod.rs
+++ b/pbs-client/src/tools/mod.rs
@@ -556,3 +556,26 @@ pub fn handle_root_with_optional_format_version_prelude<R: pxar::decoder::SeqRea
         _ => bail!("unexpected entry kind {:?}", first.kind()),
     }
 }
+
+/// Raise the soft limit for open file handles to the hard limit
+///
+/// Returns the values set before raising the limit as libc::rlimit64
+pub fn raise_nofile_limit() -> Result<libc::rlimit64, Error> {
+    let mut old = libc::rlimit64 {
+        rlim_cur: 0,
+        rlim_max: 0,
+    };
+    if 0 != unsafe { libc::getrlimit64(libc::RLIMIT_NOFILE, &mut old as *mut libc::rlimit64) } {
+        bail!("Failed to get nofile rlimit");
+    }
+
+    let mut new = libc::rlimit64 {
+        rlim_cur: old.rlim_max,
+        rlim_max: old.rlim_max,
+    };
+    if 0 != unsafe { libc::setrlimit64(libc::RLIMIT_NOFILE, &mut new as *mut libc::rlimit64) } {
+        bail!("Failed to set nofile rlimit");
+    }
+
+    Ok(old)
+}
-- 
2.39.2