unix: make uv_fs_read() fill all buffers

The fallback for systems that lack preadv() only filled the first
buffer.

This commit rectifies that to fill all (or at least as many as possible)
buffers.

Fixes: https://github.com/libuv/libuv/issues/2332
PR-URL: https://github.com/libuv/libuv/pull/2338
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Jameson Nash <vtjnash@gmail.com>
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>

.gitattributes

@@ -0,0 +1 @@
+test/fixtures/lorem_ipsum.txt text eol=lf

Makefile.am

@@ -117,6 +117,7 @@ endif  # WINNT
 
 EXTRA_DIST = test/fixtures/empty_file \
              test/fixtures/load_error.node \
+             test/fixtures/lorem_ipsum.txt \
              include \
              docs \
              img \

src/unix/fs.c

@@ -278,6 +278,54 @@ static ssize_t uv__fs_open(uv_fs_t* req) {
 }
 
 
+static ssize_t uv__fs_preadv(uv_file fd,
+                             uv_buf_t* bufs,
+                             unsigned int nbufs,
+                             off_t off) {
+  uv_buf_t* buf;
+  uv_buf_t* end;
+  ssize_t result;
+  ssize_t rc;
+  size_t pos;
+
+  assert(nbufs > 0);
+
+  result = 0;
+  pos = 0;
+  buf = bufs + 0;
+  end = bufs + nbufs;
+
+  for (;;) {
+    do
+      rc = pread(fd, buf->base + pos, buf->len - pos, off + result);
+    while (rc == -1 && errno == EINTR);
+
+    if (rc == 0)
+      break;
+
+    if (rc == -1 && result == 0)
+      return UV__ERR(errno);
+
+    if (rc == -1)
+      break;  /* We read some data so return that, ignore the error. */
+
+    pos += rc;
+    result += rc;
+
+    if (pos < buf->len)
+      continue;
+
+    pos = 0;
+    buf += 1;
+
+    if (buf == end)
+      break;
+  }
+
+  return result;
+}
+
+
 static ssize_t uv__fs_read(uv_fs_t* req) {
 #if defined(__linux__)
   static int no_preadv;
@@ -307,7 +355,7 @@ static ssize_t uv__fs_read(uv_fs_t* req) {
     if (no_preadv) retry:
 # endif
     {
-      result = pread(req->file, req->bufs[0].base, req->bufs[0].len, req->off);
+      result = uv__fs_preadv(req->file, req->bufs, req->nbufs, req->off);
     }
 # if defined(__linux__)
     else {

test/fixtures/lorem_ipsum.txt

@@ -0,0 +1 @@
+Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

test/test-fs.c

@@ -2721,6 +2721,60 @@ TEST_IMPL(fs_rename_to_existing_file) {
 }
 
 
+TEST_IMPL(fs_read_bufs) {
+  char scratch[768];
+  uv_buf_t bufs[4];
+
+  ASSERT(0 <= uv_fs_open(NULL, &open_req1,
+                         "test/fixtures/lorem_ipsum.txt",
+                         O_RDONLY, 0, NULL));
+  ASSERT(open_req1.result >= 0);
+  uv_fs_req_cleanup(&open_req1);
+
+  ASSERT(UV_EINVAL == uv_fs_read(NULL, &read_req, open_req1.result,
+                                 NULL, 0, 0, NULL));
+  ASSERT(UV_EINVAL == uv_fs_read(NULL, &read_req, open_req1.result,
+                                 NULL, 1, 0, NULL));
+  ASSERT(UV_EINVAL == uv_fs_read(NULL, &read_req, open_req1.result,
+                                 bufs, 0, 0, NULL));
+
+  bufs[0] = uv_buf_init(scratch + 0, 256);
+  bufs[1] = uv_buf_init(scratch + 256, 256);
+  bufs[2] = uv_buf_init(scratch + 512, 128);
+  bufs[3] = uv_buf_init(scratch + 640, 128);
+
+  ASSERT(446 == uv_fs_read(NULL,
+                           &read_req,
+                           open_req1.result,
+                           bufs + 0,
+                           2,  /* 2x 256 bytes. */
+                           0,  /* Positional read. */
+                           NULL));
+  ASSERT(read_req.result == 446);
+  uv_fs_req_cleanup(&read_req);
+
+  ASSERT(190 == uv_fs_read(NULL,
+                           &read_req,
+                           open_req1.result,
+                           bufs + 2,
+                           2,  /* 2x 128 bytes. */
+                           256,  /* Positional read. */
+                           NULL));
+  ASSERT(read_req.result == /* 446 - 256 */ 190);
+  uv_fs_req_cleanup(&read_req);
+
+  ASSERT(0 == memcmp(bufs[1].base + 0, bufs[2].base, 128));
+  ASSERT(0 == memcmp(bufs[1].base + 128, bufs[3].base, 190 - 128));
+
+  ASSERT(0 == uv_fs_close(NULL, &close_req, open_req1.result, NULL));
+  ASSERT(close_req.result == 0);
+  uv_fs_req_cleanup(&close_req);
+
+  MAKE_VALGRIND_HAPPY();
+  return 0;
+}
+
+
 TEST_IMPL(fs_read_file_eof) {
 #if defined(__CYGWIN__) || defined(__MSYS__)
   RETURN_SKIP("Cygwin pread at EOF may (incorrectly) return data!");

test/test-list.h

@@ -326,6 +326,7 @@ TEST_DECLARE   (fs_utime)
 TEST_DECLARE   (fs_futime)
 TEST_DECLARE   (fs_file_open_append)
 TEST_DECLARE   (fs_stat_missing_path)
+TEST_DECLARE   (fs_read_bufs)
 TEST_DECLARE   (fs_read_file_eof)
 TEST_DECLARE   (fs_event_watch_dir)
 TEST_DECLARE   (fs_event_watch_dir_recursive)
@@ -913,6 +914,7 @@ TASK_LIST_START
   TEST_ENTRY  (fs_non_symlink_reparse_point)
 #endif
   TEST_ENTRY  (fs_stat_missing_path)
+  TEST_ENTRY  (fs_read_bufs)
   TEST_ENTRY  (fs_read_file_eof)
   TEST_ENTRY  (fs_file_open_append)
   TEST_ENTRY  (fs_event_watch_dir)