early wip

wip/copyattr-test/test.c

@@ -0,0 +1,85 @@
+// vi: sw=2 tw=80
+#include <fcntl.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <sys/stat.h>
+#include <time.h>
+#include <unistd.h>
+// WIP based loosely on coreutils cp copy_reg()
+// no ACLs or xattrs or security contexts or anything
+// also no optional overwriting symlinks (yet)
+int main(void) {
+  int fd = open("test.txt", O_RDONLY /*| O_BINARY*/);
+  if(fd == -1) {
+    perror("open(in)");
+    return 1;
+  }
+  struct stat s;
+  if(fstat(fd, &s)) {
+    perror("fstat(in)");
+    close(fd);
+    return 1;
+  }
+  char b[64];
+  ssize_t c = read(fd, b, 64); // would actually be a loop
+  if(c == -1) {
+    perror("read(in)");
+    close(fd);
+    return 1;
+  }
+  if(close(fd)) {
+    perror("close(in)");
+    return 1;
+  }
+  fd = open("test2.txt", O_WRONLY /*| O_BINARY*/ | O_CREAT | O_TRUNC,
+      s.st_mode | S_IWUSR);
+  if(fd == -1) {
+    perror("open(out)");
+    return 1;
+  }
+#ifdef AVOID_CHOWN
+  struct stat o;
+  if(fstat(fd, &o)) {
+    perror("fstat(out)");
+    close(fd);
+    return 1;
+  }
+#endif
+  if(write(fd, b, c) != c) { // see read
+    perror("write(out)");
+    close(fd);
+    return 1;
+  }
+  int r = 0;
+  if(futimens(fd,
+	 offsetof(struct stat, st_mtim) - offsetof(struct stat, st_atim)
+		 == sizeof(struct timespec)
+	     ? &s.st_atim
+	     : (const struct timespec[2]){
+		   {.tv_sec = s.st_atim.tv_sec, .tv_nsec = s.st_atim.tv_nsec},
+		   {.tv_sec = s.st_mtim.tv_sec,
+		       .tv_nsec = s.st_mtim.tv_nsec}})) {
+    perror("futimens(out)");
+    r = 1;
+  }
+  if(
+#ifdef AVOID_CHOWN
+      // "Avoid calling chown if we know it's not necessary"
+      (o.st_uid != s.st_uid || o.st_gid != s.st_gid) &&
+#endif
+      fchown(fd, s.st_uid, s.st_gid)) {
+    // TODO: allow failure?
+    perror("fchown(out)");
+    r = 1;
+  }
+  if(fchmod(fd, s.st_mode)) {
+    perror("fchmod(out)");
+    r = 1;
+  }
+  // TODO: futimens last?
+  if(close(fd)) {
+    perror("close(out)");
+    r = 1;
+  }
+  return r;
+}

wip/copyattr-test/test.txt

@@ -0,0 +1 @@
+fart