[libvirt] [PATCH] iohelper: use saferead if later write with O_DIRECT
One of the usecases of iohelper is to read from pipe and write
to file with O_DIRECT. As we read from pipe we can have partial
read and then we fail to write this data because output file
is open with O_DIRECT and buffer size is not aligned.
---
src/util/iohelper.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/src/util/iohelper.c b/src/util/iohelper.c
index 5416d45..bb8a8dd 100644
--- a/src/util/iohelper.c
+++ b/src/util/iohelper.c
@@ -109,9 +109,21 @@ runIO(const char *path, int fd, int oflags)
while (1) {
ssize_t got;
- if ((got = read(fdin, buf, buflen)) < 0) {
- if (errno == EINTR)
+ /* If we read with O_DIRECT from file we can't use saferead as
+ * it can lead to unaligned read after reading last bytes.
+ * If we write with O_DIRECT use should use saferead so that
+ * writes will be aligned.
+ * In other cases using saferead reduces number of syscalls.
+ */
+ if (fdin == fd && direct) {
+ if ((got = read(fdin, buf, buflen)) < 0 &&
+ errno == EINTR)
continue;
+ } else {
+ got = saferead(fdin, buf, buflen);
+ }
+
+ if (got < 0) {
virReportSystemError(errno, _("Unable to read %s"), fdinname);
goto cleanup;
}
--
1.8.3.1