unset O_DIRECT flag on last chunk if irregular sized

src/uu/dd/src/dd.rs

@@ -4,6 +4,7 @@
 // file that was distributed with this source code.
 
 // spell-checker:ignore fname, ftype, tname, fpath, specfile, testfile, unspec, ifile, ofile, outfile, fullblock, urand, fileio, atoe, atoibm, behaviour, bmax, bremain, cflags, creat, ctable, ctty, datastructures, doesnt, etoa, fileout, fname, gnudd, iconvflags, iseek, nocache, noctty, noerror, nofollow, nolinks, nonblock, oconvflags, oseek, outfile, parseargs, rlen, rmax, rremain, rsofar, rstat, sigusr, wlen, wstat seekable oconv canonicalized fadvise Fadvise FADV DONTNEED ESPIPE bufferedoutput
+// spell-checker:ignore GETFL SETFL
 
 mod blocks;
 mod bufferedoutput;
@@ -42,6 +43,8 @@ use std::time::{Duration, Instant};
 use clap::{crate_version, Arg, Command};
 use gcd::Gcd;
 #[cfg(target_os = "linux")]
+use nix::fcntl::{fcntl, FcntlArg, OFlag};
+#[cfg(target_os = "linux")]
 use nix::{
     errno::Errno,
     fcntl::{posix_fadvise, PosixFadviseAdvice},
@@ -509,6 +512,20 @@ enum Dest {
 }
 
 impl Dest {
+    fn unset_direct(&mut self) -> io::Result<()> {
+        match self {
+            #[cfg(target_os = "linux")]
+            Self::File(f, _d) => {
+                let mut mode = OFlag::from_bits_retain(fcntl(f.as_raw_fd(), FcntlArg::F_GETFL)?);
+                mode.remove(OFlag::O_DIRECT);
+                nix::fcntl::fcntl(f.as_raw_fd(), FcntlArg::F_SETFL(mode))?;
+            }
+            _ => {}
+        }
+
+        Ok(())
+    }
+
     fn fsync(&mut self) -> io::Result<()> {
         match self {
             Self::Stdout(stdout) => stdout.flush(),
@@ -774,7 +791,14 @@ impl<'a> Output<'a> {
         let mut writes_partial = 0;
         let mut bytes_total = 0;
 
-        for chunk in buf.chunks(self.settings.obs) {
+        let chunk_size = self.settings.obs;
+        for chunk in buf.chunks(chunk_size) {
+            if (self.settings.oflags.direct) && (chunk.len() < chunk_size) {
+                // in case of direct io, only buffers with chunk_size are accepted.
+                // thus, for writing a (last) buffer with irregular length, we need to switch off the direct io.
+                self.dst.unset_direct()?;
+            }
+
             let wlen = self.dst.write(chunk)?;
             if wlen < self.settings.obs {
                 writes_partial += 1;

tests/by-util/test_dd.rs

@@ -1713,3 +1713,26 @@ fn test_reading_partial_blocks_from_fifo_unbuffered() {
     let expected = b"0+2 records in\n0+2 records out\n4 bytes copied";
     assert!(output.stderr.starts_with(expected));
 }
+
+#[test]
+fn test_reading_and_writing_with_direct_flag_from_and_to_files_with_irregular_size() {
+    let ts = TestScenario::new(util_name!());
+    let at = &ts.fixtures;
+
+    ts.ccmd("truncate").args(&["-s", "511", "short"]).succeeds();
+    ts.ccmd("truncate").args(&["-s", "8192", "in"]).succeeds();
+    ts.ccmd("truncate").args(&["-s", "8191", "m1"]).succeeds();
+    ts.ccmd("truncate").args(&["-s", "8193", "p1"]).succeeds();
+
+    ts.ucmd()
+        .args(&["if=in", "oflag=direct", "of=out"])
+        .succeeds();
+
+    for testfile in ["short", "m1", "p1"] {
+        at.remove("out");
+        ts.ucmd()
+            .arg(format!("if={testfile}"))
+            .args(&["iflag=direct", "oflag=direct", "of=out"])
+            .succeeds();
+    }
+}