[pbs-devel] [PATCH proxmox v2] tools: Add tempfile() helper function

[Fabian Grünbichler]

On August 12, 2020 4:34 pm, Mira Limbeck wrote:
> 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>
> ---
>  proxmox/src/tools/fs.rs | 25 ++++++++++++++++++++++++-
>  1 file changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/proxmox/src/tools/fs.rs b/proxmox/src/tools/fs.rs
> index b1a95b5..b3072db 100644
> --- a/proxmox/src/tools/fs.rs
> +++ b/proxmox/src/tools/fs.rs
> @@ -3,6 +3,7 @@
>  use std::ffi::CStr;
>  use std::fs::{File, OpenOptions};
>  use std::io::{self, BufRead, BufReader, Write};
> +use std::os::unix::fs::OpenOptionsExt;
>  use std::os::unix::io::{AsRawFd, FromRawFd, RawFd};
>  use std::path::Path;
>  use std::time::Duration;
> @@ -11,7 +12,7 @@ use anyhow::{bail, format_err, Error};
>  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 +519,25 @@ pub fn open_file_locked<P: AsRef<Path>>(path: P, timeout: Duration) -> Result<Fi
>          Err(err) => bail!("Unable to acquire lock {:?} - {}", path, err),
>      }
>  }
> +
> +/// 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> {
> +    match std::fs::OpenOptions::new()
> +        .write(true)
> +        .read(true)
> +        .custom_flags(libc::O_TMPFILE)
> +        .open("/tmp")
> +    {
> +        Ok(file) => return Ok(file),
> +        Err(err) => {
> +            eprintln!(
> +                "Error creating tempfile: '{}', trying mkstemp() instead",
> +                err
> +            );

print this once, cache result, always use fallback until restart if 
needed?

also, can we decide based on the error if we even want/can 
fallback? e.g., /tmp might have strange permissions? the man page states 
that open should return EISDIR in case O_TMPFILE is not supported..

> +            let (fd, path) = mkstemp("/tmp/proxmox-tmpfile_XXXXXX")?;

I'd still like this to be in a sub-directory (owned by 'backup'), even 
if it should be unproblematic..

> +            unlink(path.as_path())?;
> +            let file = unsafe { File::from_raw_fd(fd) };
> +            Ok(file)
> +        }
> +    }
> +}
> -- 
> 2.20.1
> 
> 
> 
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