tools/libxc: pass errno to callers of xc_domain_save

Callers of xc_domain_save use errno to print diagnostics if the call
fails. But xc_domain_save does not preserve the actual errno in case of
a failure.

This change preserves errno in all cases where code jumps to the label
"out". In addition a new label "exit" is added to catch also code which
used to do just "return 1".

Now libxl_save_helper:complete can print the actual error string.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/libxc/xc_domain_save.c

@@ -25,6 +25,7 @@
 #include <stdlib.h>
 #include <unistd.h>
 #include <sys/time.h>
+#include <assert.h>
 
 #include "xc_private.h"
 #include "xc_bitops.h"
@@ -150,6 +151,7 @@ static inline int outbuf_write(xc_interface *xch,
                                struct outbuf* ob, void* buf, size_t len)
 {
     if ( len > ob->size - ob->pos ) {
+        errno = ERANGE;
         DBGPRINTF("outbuf_write: %zu > %zu@%zu\n", len, ob->size - ob->pos, ob->pos);
         return -1;
     }
@@ -806,7 +808,7 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t dom, uint32_t max_iter
     xc_dominfo_t info;
     DECLARE_DOMCTL;
 
-    int rc = 1, frc, i, j, last_iter = 0, iter = 0;
+    int rc, frc, i, j, last_iter = 0, iter = 0;
     int live  = (flags & XCFLAGS_LIVE);
     int debug = (flags & XCFLAGS_DEBUG);
     int superpages = !!hvm;
@@ -899,7 +901,7 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t dom, uint32_t max_iter
     {
         ERROR("No switch_qemu_logdirty callback provided.");
         errno = EINVAL;
-        return 1;
+        goto exit;
     }
 
     outbuf_init(xch, &ob_pagebuf, OUTBUF_SIZE);
@@ -914,13 +916,13 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t dom, uint32_t max_iter
                             &ctx->max_mfn, &ctx->hvirt_start, &ctx->pt_levels, &dinfo->guest_width) )
     {
         ERROR("Unable to get platform info.");
-        return 1;
+        goto exit;
     }
 
     if ( xc_domain_getinfo(xch, dom, 1, &info) != 1 )
     {
         PERROR("Could not get domain info");
-        return 1;
+        goto exit;
     }
 
     shared_info_frame = info.shared_info_frame;
@@ -942,6 +944,7 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t dom, uint32_t max_iter
 
     if ( dinfo->p2m_size > ~XEN_DOMCTL_PFINFO_LTAB_MASK )
     {
+        errno = E2BIG;
         ERROR("Cannot save this big a guest");
         goto out;
     }
@@ -1012,6 +1015,7 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t dom, uint32_t max_iter
 
     if ( !to_send || !to_fix || !to_skip )
     {
+        errno = ENOMEM;
         ERROR("Couldn't allocate to_send array");
         goto out;
     }
@@ -1030,6 +1034,7 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t dom, uint32_t max_iter
         hvm_buf = malloc(hvm_buf_size);
         if ( !hvm_buf )
         {
+            errno = ENOMEM;
             ERROR("Couldn't allocate memory");
             goto out;
         }
@@ -1598,6 +1603,7 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t dom, uint32_t max_iter
 
         if ( info.max_vcpu_id >= XC_SR_MAX_VCPUS )
         {
+            errno = E2BIG;
             ERROR("Too many VCPUS in guest!");
             goto out;
         }
@@ -1830,7 +1836,7 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t dom, uint32_t max_iter
         }
         
         /* HVM guests are done now */
-        rc = 0;
+        errno = 0;
         goto out;
     }
 
@@ -1888,6 +1894,7 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t dom, uint32_t max_iter
     mfn = GET_FIELD(&ctxt, user_regs.edx);
     if ( !MFN_IS_IN_PSEUDOPHYS_MAP(mfn) )
     {
+        errno = ERANGE;
         ERROR("Suspend record is not in range of pseudophys map");
         goto out;
     }
@@ -1910,6 +1917,7 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t dom, uint32_t max_iter
             mfn = GET_FIELD(&ctxt, gdt_frames[j]);
             if ( !MFN_IS_IN_PSEUDOPHYS_MAP(mfn) )
             {
+                errno = ERANGE;
                 ERROR("GDT frame is not in range of pseudophys map");
                 goto out;
             }
@@ -1920,6 +1928,7 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t dom, uint32_t max_iter
         if ( !MFN_IS_IN_PSEUDOPHYS_MAP(UNFOLD_CR3(
                                            GET_FIELD(&ctxt, ctrlreg[3]))) )
         {
+            errno = ERANGE;
             ERROR("PT base is not in range of pseudophys map");
             goto out;
         }
@@ -1931,6 +1940,7 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t dom, uint32_t max_iter
         {
             if ( !MFN_IS_IN_PSEUDOPHYS_MAP(UNFOLD_CR3(ctxt.x64.ctrlreg[1])) )
             {
+                errno = ERANGE;
                 ERROR("PT base is not in range of pseudophys map");
                 goto out;
             }
@@ -2027,9 +2037,13 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t dom, uint32_t max_iter
     }
 
     /* Success! */
-    rc = 0;
+    rc = errno = 0;
+    goto out_rc;
 
  out:
+    rc = errno;
+    assert(rc);
+ out_rc:
     completed = 1;
 
     if ( !rc && callbacks->postcopy )
@@ -2044,13 +2058,11 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t dom, uint32_t max_iter
         if (wrcompressed(io_fd) < 0)
         {
             ERROR("Error when writing compressed data, after postcopy\n");
-            rc = 1;
             goto out;
         }
         /* Append the tailbuf data to the main outbuf */
         if ( wrexact(io_fd, ob_tailbuf.buf, ob_tailbuf.pos) )
         {
-            rc = 1;
             PERROR("Error when copying tailbuf into outbuf");
             goto out;
         }
@@ -2059,7 +2071,8 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t dom, uint32_t max_iter
     /* Flush last write and discard cache for file. */
     if ( ob && outbuf_flush(xch, ob, io_fd) < 0 ) {
         PERROR("Error when flushing output buffer");
-        rc = 1;
+        if (!rc)
+            rc = errno;
     }
 
     discard_file_cache(xch, io_fd, 1 /* flush */);
@@ -2074,7 +2087,6 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t dom, uint32_t max_iter
         /* reset stats timer */
         print_stats(xch, dom, 0, &time_stats, &shadow_stats, 0);
 
-        rc = 1;
         /* last_iter = 1; */
         if ( suspend_and_state(callbacks->suspend, callbacks->data, xch,
                                io_fd, dom, &info) )
@@ -2130,9 +2142,11 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t dom, uint32_t max_iter
     free(hvm_buf);
     outbuf_free(&ob_pagebuf);
 
-    DPRINTF("Save exit of domid %u with rc=%d\n", dom, rc);
+    errno = rc;
+exit:
+    DPRINTF("Save exit of domid %u with errno=%d\n", dom, errno);
 
-    return !!rc;
+    return !!errno;
 }
 
 /*