[Xen-API] [PATCH 3 of 5 v3] tools/libxc: Implement xc_readconsolering_buffer()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Functions identically to xc_readconsolering(), but uses a user-provided
xc_hypercall_buffer_t to save using a bounce buffer.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

--
Changes since v2:
 * Document xc_readconsolering() and xc_readconsolering_buffer() functions
Changes since v1:
 * Reduce xc_readconsolering() to use xc_readconsolering_buffer()

diff -r 0bd32c19873e -r c7b82dfbec34 tools/libxc/xc_misc.c
--- a/tools/libxc/xc_misc.c
+++ b/tools/libxc/xc_misc.c
@@ -70,13 +70,29 @@ int xc_readconsolering(xc_interface *xch
                        int clear, int incremental, uint32_t *pindex)
 {
     int ret;
-    unsigned int nr_chars = *pnr_chars;
-    DECLARE_SYSCTL;
-    DECLARE_HYPERCALL_BOUNCE(buffer, nr_chars, XC_HYPERCALL_BUFFER_BOUNCE_OUT);
+    DECLARE_HYPERCALL_BOUNCE(buffer, *pnr_chars, 
XC_HYPERCALL_BUFFER_BOUNCE_OUT);
 
     if ( xc_hypercall_bounce_pre(xch, buffer) )
         return -1;
 
+    ret = xc_readconsolering_buffer(xch, HYPERCALL_BUFFER(buffer),
+                                    pnr_chars, clear, incremental, pindex);
+
+    xc_hypercall_bounce_post(xch, buffer);
+
+    return ret;
+}
+
+int xc_readconsolering_buffer(xc_interface *xch,
+                              xc_hypercall_buffer_t *buffer,
+                              unsigned int *pnr_chars,
+                              int clear, int incremental, uint32_t *pindex)
+{
+    int ret;
+    unsigned int nr_chars = *pnr_chars;
+    DECLARE_SYSCTL;
+    DECLARE_HYPERCALL_BUFFER_ARGUMENT(buffer);
+
     sysctl.cmd = XEN_SYSCTL_readconsole;
     set_xen_guest_handle(sysctl.u.readconsole.buffer, buffer);
     sysctl.u.readconsole.count = nr_chars;
@@ -95,8 +111,6 @@ int xc_readconsolering(xc_interface *xch
             *pindex = sysctl.u.readconsole.index;
     }
 
-    xc_hypercall_bounce_post(xch, buffer);
-
     return ret;
 }
 
diff -r 0bd32c19873e -r c7b82dfbec34 tools/libxc/xenctrl.h
--- a/tools/libxc/xenctrl.h
+++ b/tools/libxc/xenctrl.h
@@ -994,10 +994,26 @@ int xc_physdev_pci_access_modify(xc_inte
                                  int func,
                                  int enable);
 
+/*
+ * For both readconsolering functions, *pnr_chars is both an input and
+ * output.  As an input, it specifies the size of *buffer, and as an output
+ * indicates now many character Xen wrote into *buffer.
+ *
+ * The 'clear' parameter indicates whether Xen should clear the buffer or not.
+ * If incremental is set, *pindex is an input and output parameter to aid with
+ * sequential small reads of the console ring.
+ *
+ * xc_readconsolering_buffer is preferred to avoid an extra copy of the console
+ * ring buffer.
+ */
 int xc_readconsolering(xc_interface *xch,
                        char *buffer,
                        unsigned int *pnr_chars,
                        int clear, int incremental, uint32_t *pindex);
+int xc_readconsolering_buffer(xc_interface *xch,
+                              xc_hypercall_buffer_t *buffer,
+                              unsigned int *pnr_chars,
+                              int clear, int incremental, uint32_t *pindex);
 int xc_consoleringsize(xc_interface *xch, uint64_t *psize);
 
 int xc_send_debug_keys(xc_interface *xch, char *keys);

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