[PATCH 22/29] tools/libxl: Allow limiting amount copied by datacopier

[Andrew Cooper <andrew.cooper3@citrix.com>]

From: Ross Lagerwall <ross.lagerwall@citrix.com>

Add a parameter, maxread, to limit the amount of data read from the
source fd of a datacopier.

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
---
 tools/libxl/libxl_aoutils.c    |    9 +++++++--
 tools/libxl/libxl_bootloader.c |    2 ++
 tools/libxl/libxl_dom.c        |    1 +
 tools/libxl/libxl_internal.h   |    1 +
 4 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/tools/libxl/libxl_aoutils.c b/tools/libxl/libxl_aoutils.c
index caba637..6502325 100644
--- a/tools/libxl/libxl_aoutils.c
+++ b/tools/libxl/libxl_aoutils.c
@@ -145,7 +145,7 @@ static void datacopier_check_state(libxl__egc *egc, libxl__datacopier_state *dc)
                 return;
             }
         }
-    } else if (!libxl__ev_fd_isregistered(&dc->toread)) {
+    } else if (!libxl__ev_fd_isregistered(&dc->toread) || dc->maxread == 0) {
         /* we have had eof */
         datacopier_callback(egc, dc, 0, 0);
         return;
@@ -233,7 +233,8 @@ static void datacopier_readable(libxl__egc *egc, libxl__ev_fd *ev,
         }
         int r = read(ev->fd,
                      buf->buf + buf->used,
-                     sizeof(buf->buf) - buf->used);
+                     (sizeof(buf->buf) - buf->used) < dc->maxread ?
+                         (sizeof(buf->buf) - buf->used) : dc->maxread);
         if (r < 0) {
             if (errno == EINTR) continue;
             if (errno == EWOULDBLOCK) break;
@@ -258,7 +259,11 @@ static void datacopier_readable(libxl__egc *egc, libxl__ev_fd *ev,
         }
         buf->used += r;
         dc->used += r;
+        dc->maxread -= r;
         assert(buf->used <= sizeof(buf->buf));
+        assert(dc->maxread >= 0);
+        if (dc->maxread == 0)
+            break;
     }
     datacopier_check_state(egc, dc);
 }
diff --git a/tools/libxl/libxl_bootloader.c b/tools/libxl/libxl_bootloader.c
index 79947d4..1503101 100644
--- a/tools/libxl/libxl_bootloader.c
+++ b/tools/libxl/libxl_bootloader.c
@@ -516,6 +516,7 @@ static void bootloader_gotptys(libxl__egc *egc, libxl__openpty_state *op)
 
     bl->keystrokes.ao = ao;
     bl->keystrokes.maxsz = BOOTLOADER_BUF_OUT;
+    bl->keystrokes.maxread = INT_MAX;
     bl->keystrokes.copywhat =
         GCSPRINTF("bootloader input for domain %"PRIu32, bl->domid);
     bl->keystrokes.callback =         bootloader_keystrokes_copyfail;
@@ -527,6 +528,7 @@ static void bootloader_gotptys(libxl__egc *egc, libxl__openpty_state *op)
 
     bl->display.ao = ao;
     bl->display.maxsz = BOOTLOADER_BUF_IN;
+    bl->display.maxread = INT_MAX;
     bl->display.copywhat =
         GCSPRINTF("bootloader output for domain %"PRIu32, bl->domid);
     bl->display.callback =         bootloader_display_copyfail;
diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
index 0dfdb08..2f74341 100644
--- a/tools/libxl/libxl_dom.c
+++ b/tools/libxl/libxl_dom.c
@@ -1717,6 +1717,7 @@ void libxl__domain_save_device_model(libxl__egc *egc,
     dc->readfd = -1;
     dc->writefd = fd;
     dc->maxsz = INT_MAX;
+    dc->maxread = INT_MAX;
     dc->copywhat = GCSPRINTF("qemu save file for domain %"PRIu32, dss->domid);
     dc->writewhat = "save/migration stream";
     dc->callback = save_device_model_datacopier_done;
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 03e9978..d93a6ee 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -2425,6 +2425,7 @@ struct libxl__datacopier_state {
     libxl__ao *ao;
     int readfd, writefd;
     ssize_t maxsz;
+    ssize_t maxread;
     const char *copywhat, *readwhat, *writewhat; /* for error msgs */
     FILE *log; /* gets a copy of everything */
     libxl__datacopier_callback *callback;
-- 
1.7.10.4