file-posix: Fix EINTR handling

EINTR should be checked against errno, not ret. While fixing the bug,
collect the branches with a switch block.

Also, change the return value from -ENOSTUP to -ENOSPC when the actual
issue is request range passes EOF, which should be distinguishable from
the case of error == ENOSYS by the caller, so that it could still retry
with other byte ranges, whereas it shouldn't retry anymore upon ENOSYS.
Signed-off-by: NFam Zheng <famz@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/file-posix.c

@@ -1488,20 +1488,21 @@ static ssize_t handle_aiocb_copy_range(RawPosixAIOData *aiocb)
         ssize_t ret = copy_file_range(aiocb->aio_fildes, &in_off,
                                       aiocb->aio_fd2, &out_off,
                                       bytes, 0);
-        if (ret == -EINTR) {
-            continue;
+        if (ret == 0) {
+            /* No progress (e.g. when beyond EOF), let the caller fall back to
+             * buffer I/O. */
+            return -ENOSPC;
         }
         if (ret < 0) {
-            if (errno == ENOSYS) {
+            switch (errno) {
+            case ENOSYS:
                 return -ENOTSUP;
-            } else {
+            case EINTR:
+                continue;
+            default:
                 return -errno;
             }
         }
-        if (!ret) {
-            /* No progress (e.g. when beyond EOF), fall back to buffer I/O. */
-            return -ENOTSUP;
-        }
         bytes -= ret;
     }
     return 0;