cp: use lstat for destination check to support LD_PRELOAD tests

Author: ChrisDryden

bench_skip_buffer.sh

@@ -0,0 +1,91 @@
+#!/bin/bash
+# Benchmark: Compare old vs new dd skip implementation
+#
+# OLD: Uses io::copy + BufReader (internal 8KB chunks regardless of ibs)
+# NEW: Uses direct read loop with ibs-sized buffer (matches GNU dd)
+
+set -e
+
+GNU_DD="/bin/dd"
+OLD_DD="/tmp/dd_old"
+NEW_DD="/tmp/dd_new"
+
+echo "=============================================="
+echo "DD Skip Buffer Implementation Comparison"
+echo "=============================================="
+echo ""
+echo "Comparing three implementations:"
+echo "  GNU dd:  Reference implementation"
+echo "  OLD:     io::copy + BufReader (before this PR)"
+echo "  NEW:     Direct read with ibs-sized buffer (this PR)"
+echo ""
+
+count_stdin_reads() {
+    local dd_cmd="$1"
+    local ibs="$2"
+    local skip_bytes=$((10 * 1024 * 1024))  # 10MB
+    local skip_blocks=$((skip_bytes / ibs))
+    cat /dev/zero | strace -e read "$dd_cmd" ibs=$ibs skip=$skip_blocks count=1 of=/dev/null 2>&1 | grep -c "^read(0"
+}
+
+show_read_request() {
+    local dd_cmd="$1"
+    local ibs="$2"
+    local skip_bytes=$((1 * 1024 * 1024))  # 1MB
+    local skip_blocks=$((skip_bytes / ibs))
+    # Show the size requested in the read() call
+    cat /dev/zero | strace -e read "$dd_cmd" ibs=$ibs skip=$skip_blocks count=1 of=/dev/null 2>&1 | grep "^read(0" | head -1 | sed 's/.*,\s*\([0-9]*\)).*/\1/'
+}
+
+echo "=============================================="
+echo "Test 1: Read Request Size (what size buffer is used)"
+echo "=============================================="
+echo ""
+echo "This shows the 3rd argument to read() - the buffer size requested."
+echo "GNU dd uses ibs. OLD used fixed size. NEW should match GNU."
+echo ""
+
+printf "%-12s %-15s %-15s %-15s\n" "ibs" "GNU dd" "OLD (before)" "NEW (after)"
+printf "%-12s %-15s %-15s %-15s\n" "---" "------" "-----------" "----------"
+
+for ibs in 512 8192 1048576; do
+    gnu_size=$(show_read_request "$GNU_DD" "$ibs")
+    old_size=$(show_read_request "$OLD_DD" "$ibs")
+    new_size=$(show_read_request "$NEW_DD" "$ibs")
+    printf "%-12s %-15s %-15s %-15s\n" "$ibs" "$gnu_size" "$old_size" "$new_size"
+done
+
+echo ""
+echo "=============================================="
+echo "Test 2: Syscall Count (skipping 10MB)"
+echo "=============================================="
+echo ""
+echo "Fewer syscalls = more efficient (for large ibs)."
+echo "More syscalls = correct behavior (for small ibs)."
+echo ""
+
+printf "%-12s %-10s %-12s %-15s %-15s\n" "ibs" "Expected" "GNU dd" "OLD (before)" "NEW (after)"
+printf "%-12s %-10s %-12s %-15s %-15s\n" "---" "--------" "------" "-----------" "----------"
+
+for ibs in 512 8192 65536; do
+    expected=$((10 * 1024 * 1024 / ibs))
+    gnu_count=$(count_stdin_reads "$GNU_DD" "$ibs")
+    old_count=$(count_stdin_reads "$OLD_DD" "$ibs")
+    new_count=$(count_stdin_reads "$NEW_DD" "$ibs")
+    printf "%-12s %-10s %-12s %-15s %-15s\n" "$ibs" "~$expected" "$gnu_count" "$old_count" "$new_count"
+done
+
+echo ""
+echo "=============================================="
+echo "Analysis"
+echo "=============================================="
+echo ""
+echo "OLD behavior (io::copy + BufReader):"
+echo "  - Always used ~8KB internal buffer regardless of ibs"
+echo "  - ~1,280 syscalls for 10MB regardless of ibs setting"
+echo "  - Did NOT match GNU dd behavior"
+echo ""
+echo "NEW behavior (direct read with ibs buffer):"
+echo "  - Uses ibs-sized buffer as specified by user"
+echo "  - Syscall count scales with ibs (matches GNU dd)"
+echo "  - Correctly implements dd semantics"

src/uu/cp/src/cp.rs

@@ -1390,8 +1390,7 @@ pub fn copy(sources: &[PathBuf], target: &Path, options: &Options) -> CopyResult
             let dest = construct_dest_path(source, target, target_type, options)
                 .unwrap_or_else(|_| target.to_path_buf());
 
-            if fs::metadata(&dest).is_ok()
-                && !fs::symlink_metadata(&dest)?.file_type().is_symlink()
+            if FileInformation::from_path(&dest, false).is_ok_and(|info| !info.is_symlink())
                 // if both `source` and `dest` are symlinks, it should be considered as an overwrite.
                 || fs::metadata(source).is_ok()
                     && fs::symlink_metadata(source)?.file_type().is_symlink()

src/uucore/src/lib/features/fs.rs

@@ -166,6 +166,16 @@ impl FileInformation {
         #[cfg(any(target_os = "netbsd", not(target_pointer_width = "64")))]
         return self.0.st_ino.into();
     }
+
+    #[cfg(unix)]
+    pub fn is_symlink(&self) -> bool {
+        (self.0.st_mode as mode_t & S_IFMT) == S_IFLNK
+    }
+
+    #[cfg(windows)]
+    pub fn is_symlink(&self) -> bool {
+        (self.0.file_attributes() & windows_sys::Win32::Storage::FileSystem::FILE_ATTRIBUTE_REPARSE_POINT) != 0
+    }
 }
 
 #[cfg(unix)]

util/fetch-gnu.sh

@@ -7,6 +7,7 @@ curl -L "${repo}/releases/download/v${ver}/coreutils-${ver}.tar.xz" | tar --stri
 curl -L ${repo}/raw/refs/heads/master/tests/mv/hardlink-case.sh > tests/mv/hardlink-case.sh
 curl -L ${repo}/raw/refs/heads/master/tests/mkdir/writable-under-readonly.sh > tests/mkdir/writable-under-readonly.sh
 curl -L ${repo}/raw/refs/heads/master/tests/cp/cp-mv-enotsup-xattr.sh > tests/cp/cp-mv-enotsup-xattr.sh #spell-checker:disable-line
+curl -L ${repo}/raw/refs/heads/master/tests/cp/nfs-removal-race.sh > tests/cp/nfs-removal-race.sh
 curl -L ${repo}/raw/refs/heads/master/tests/csplit/csplit-io-err.sh > tests/csplit/csplit-io-err.sh
 # Avoid incorrect PASS
 curl -L ${repo}/raw/refs/heads/master/tests/runcon/runcon-compute.sh > tests/runcon/runcon-compute.sh