[pbs-devel] [PATCH v3 proxmox] Add tempfile() helper function

[Mira Limbeck]

The tempfile() helper function tries to create a temporary file in /tmp
with the O_TMPFILE option. If that fails it falls back to using
mkstemp().

As O_TMPFILE was introduced in kernel 3.11 this fallback can help with
CentOS 7 and its 3.10 kernel as well as with WSL (Windows Subsystem for
Linux).

Signed-off-by: Mira Limbeck <m.limbeck at proxmox.com>
---
v3:
    - O_TMPFILE support is tested on first run of tempfile()
    - EISDIR is handled specifically to test for O_TMPFILE support
    - AtomicBool is used as it provides a safe interface, but 'static mut'
        could also be used
    - mkstemp() now creates the tempfile in a subdirectory called
      proxmox-backup-<UID>

 proxmox/src/tools/fs.rs | 62 +++++++++++++++++++++++++++++++++++++++--
 1 file changed, 60 insertions(+), 2 deletions(-)

diff --git a/proxmox/src/tools/fs.rs b/proxmox/src/tools/fs.rs
index b1a95b5..0a12254 100644
--- a/proxmox/src/tools/fs.rs
+++ b/proxmox/src/tools/fs.rs
@@ -1,17 +1,20 @@
 //! File related utilities such as `replace_file`.
 
 use std::ffi::CStr;
-use std::fs::{File, OpenOptions};
+use std::fs::{DirBuilder, File, OpenOptions};
 use std::io::{self, BufRead, BufReader, Write};
+use std::os::unix::fs::{DirBuilderExt, OpenOptionsExt};
 use std::os::unix::io::{AsRawFd, FromRawFd, RawFd};
 use std::path::Path;
+use std::sync::atomic::{AtomicBool, Ordering};
 use std::time::Duration;
 
 use anyhow::{bail, format_err, Error};
+use lazy_static::lazy_static;
 use nix::errno::Errno;
 use nix::fcntl::OFlag;
 use nix::sys::stat;
-use nix::unistd::{self, Gid, Uid};
+use nix::unistd::{self, mkstemp, unlink, Gid, Uid};
 use serde_json::Value;
 
 use crate::sys::error::SysResult;
@@ -518,3 +521,58 @@ pub fn open_file_locked<P: AsRef<Path>>(path: P, timeout: Duration) -> Result<Fi
         Err(err) => bail!("Unable to acquire lock {:?} - {}", path, err),
     }
 }
+
+static O_TMPFILE_SUPPORT: AtomicBool = AtomicBool::new(true);
+lazy_static! {
+    static ref MKSTEMP_PATH: String = {
+        use nix::unistd::geteuid;
+        let uid = geteuid();
+        format!("/tmp/proxmox-backup-{}", uid)
+    };
+    static ref MKSTEMP_FILE: String = {
+        format!("{}/tmpfile_XXXXXX", MKSTEMP_PATH.as_str())
+    };
+}
+
+/// Create a new tempfile by using O_TMPFILE with a fallback to mkstemp() if it fails (e.g. not supported).
+pub fn tempfile() -> Result<File, Error> {
+    if O_TMPFILE_SUPPORT.load(Ordering::Relaxed) {
+        match std::fs::OpenOptions::new()
+            .write(true)
+            .read(true)
+            .custom_flags(libc::O_TMPFILE)
+            .open("/tmp")
+            {
+                Ok(file) => return Ok(file),
+                Err(err) => {
+                    let raw_os_error = match err.raw_os_error() {
+                        Some(v) => v,
+                        None => -1,
+                    };
+                    if raw_os_error == 21 {
+                        O_TMPFILE_SUPPORT.store(false, Ordering::Relaxed);
+                        eprintln!(
+                            "Error creating tempfile: 'EISDIR', falling back to mkstemp() instead",
+                        );
+                    } else {
+                        bail!("Error creating tempfile: '{}'", err);
+                    }
+                }
+            }
+    }
+
+
+    match DirBuilder::new().recursive(true).mode(0o700).create(MKSTEMP_PATH.as_str()) {
+        Err(err) => {
+            if err.kind() != std::io::ErrorKind::AlreadyExists {
+                bail!("Error creating directory: '{}'", MKSTEMP_PATH.as_str());
+            }
+            // ignore EEXISTS
+        },
+        _ => {},
+    }
+    let (fd, path) = mkstemp(MKSTEMP_FILE.as_str())?;
+    unlink(path.as_path())?;
+    let file = unsafe { File::from_raw_fd(fd) };
+    Ok(file)
+}
-- 
2.20.1