tweak comment

diff --git a/lib/safe-read.c b/lib/safe-read.c
index 527653c5cc7e6bd0fbdf0e2cd6761162b672dd04..e52326eaf6ccf0d3da365f669570a790f1d0f752 100644 (file)
--- a/lib/safe-read.c
+++ b/lib/safe-read.c
@@ -33,6 +33,12 @@
 extern int errno;
 #endif
 
+#ifdef EINTR
+# define IS_EINTR(x) ((x) == EINTR)
+#else
+# define IS_EINTR(x) 0
+#endif
+
 #include <limits.h>
 
 #ifndef CHAR_BIT
@@ -51,38 +57,27 @@ extern int errno;
 # define INT_MAX TYPE_MAXIMUM (int)
 #endif
 
-/* We don't pass an nbytes count > SSIZE_MAX to read() - POSIX says the
-   effect would be implementation-defined.  Also we don't pass an nbytes
-   count > INT_MAX but <= SSIZE_MAX to read() - this triggers a bug in
-   Tru64 5.1.  */
-#define MAX_BYTES_TO_READ INT_MAX
-
-#ifndef EINTR
-/* If a system doesn't have support for EINTR, define it
-   to be a value to which errno will never be set.  */
-# define EINTR (INT_MAX - 10)
-#endif
-
 /* Read up to COUNT bytes at BUF from descriptor FD, retrying if interrupted.
    Return the actual number of bytes read, zero for EOF, or SAFE_READ_ERROR
    upon error.  */
 size_t
 safe_read (int fd, void *buf, size_t count)
 {
-  size_t nbytes_to_read = count;
   ssize_t result;
 
-  /* Limit the number of bytes to read, to avoid running
-     into unspecified behaviour.  But keep the file pointer block
-     aligned when doing so.  */
-  if (nbytes_to_read > MAX_BYTES_TO_READ)
-    nbytes_to_read = MAX_BYTES_TO_READ & ~8191;
+  /* POSIX limits COUNT to SSIZE_MAX, but we limit it further, requiring
+     that COUNT <= INT_MAX, to avoid triggering a bug in Tru64 5.1.
+     When decreasing COUNT, keep the file pointer block-aligned.
+     Note that in any case, read may succeed, yet read fewer than COUNT
+     bytes, so the caller must be prepared to handle partial results.  */
+  if (count > INT_MAX)
+    count = INT_MAX & ~8191;
 
   do
     {
-      result = read (fd, buf, nbytes_to_read);
+      result = read (fd, buf, count);
     }
-  while (result < 0 && errno == EINTR);
+  while (result < 0 && IS_EINTR (errno));
 
   return (size_t) result;
 }