libxl: introduce libxl_fd_set_nonblock, rationalise _cloexec

We want a function for setting fds to nonblocking, so introduce one.

This is a very similar requirement to that for libxl_fd_set_cloexec,
so make it common with that.

While we're at it, fix a few deficiences that make this latter
function less desirable than it could be:
 * Change the return from 0/-1 (like a syscall) to a libxl error code
 * Take a boolean parameter for turning the flag on and off
 * Log on error (and so, take a ctx for this purpose)

Change callers of libxl_fd_set_cloexec to notice errors.  (Although,
such errors are highly unlikely.)

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Jackson <Ian.Jackson@eu.citrix.com>

tools/libxl/libxl.c

@@ -3658,19 +3658,38 @@ int libxl_cpupool_movedomain(libxl_ctx *ctx, uint32_t poolid, uint32_t domid)
     return 0;
 }
 
-int libxl_fd_set_cloexec(int fd)
+static int fd_set_flags(libxl_ctx *ctx, int fd,
+                        int fcntlgetop, int fcntlsetop, const char *fl,
+                        int flagmask, int set_p)
 {
-    int flags = 0;
+    int flags, r;
 
-    if ((flags = fcntl(fd, F_GETFD)) == -1) {
-        flags = 0;
+    flags = fcntl(fd, fcntlgetop);
+    if (flags == -1) {
+        LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR, "fcntl(,F_GET%s) failed",fl);
+        return ERROR_FAIL;
     }
-    if ((flags & FD_CLOEXEC)) {
-        return 0;
+
+    if (set_p)
+        flags |= flagmask;
+    else
+        flags &= ~flagmask;
+
+    r = fcntl(fd, fcntlsetop, flags);
+    if (r == -1) {
+        LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR, "fcntl(,F_SET%s) failed",fl);
+        return ERROR_FAIL;
     }
-    return fcntl(fd, F_SETFD, flags | FD_CLOEXEC);
+
+    return 0;
 }
 
+int libxl_fd_set_cloexec(libxl_ctx *ctx, int fd, int cloexec)
+  { return fd_set_flags(ctx,fd, F_GETFD,F_SETFD,"FD", FD_CLOEXEC, cloexec); }
+
+int libxl_fd_set_nonblock(libxl_ctx *ctx, int fd, int nonblock)
+  { return fd_set_flags(ctx,fd, F_GETFL,F_SETFL,"FL", O_NONBLOCK, nonblock); }
+
 /*
  * Local variables:
  * mode: C

tools/libxl/libxl.h

@@ -613,7 +613,12 @@ const char *libxl_run_dir_path(void);
 const char *libxl_xenpaging_dir_path(void);
 
 /* misc */
-int libxl_fd_set_cloexec(int fd);
+
+/* Each of these sets or clears the flag according to whether the
+ * 2nd parameter is nonzero.  On failure, they log, and
+ * return ERROR_FAIL, but also leave errno valid. */
+int libxl_fd_set_cloexec(libxl_ctx *ctx, int fd, int cloexec);
+int libxl_fd_set_nonblock(libxl_ctx *ctx, int fd, int nonblock);
 
 #include <libxl_event.h>
 

tools/libxl/libxl_qmp.c

@@ -325,7 +325,8 @@ static int qmp_open(libxl__qmp_handler *qmp, const char *qmp_socket_path,
     if (fcntl(qmp->qmp_fd, F_SETFL, flags | O_NONBLOCK) == -1) {
         return -1;
     }
-    libxl_fd_set_cloexec(qmp->qmp_fd);
+    ret = libxl_fd_set_cloexec(qmp->ctx, qmp->qmp_fd, 1);
+    if (ret) return -1;
 
     memset(&qmp->addr, 0, sizeof (&qmp->addr));
     qmp->addr.sun_family = AF_UNIX;

tools/libxl/xl_cmdimpl.c

@@ -1509,7 +1509,8 @@ static int create_domain(struct domain_create *dom_info)
             restore_fd = migrate_fd;
         } else {
             restore_fd = open(restore_file, O_RDONLY);
-            libxl_fd_set_cloexec(restore_fd);
+            rc = libxl_fd_set_cloexec(ctx, restore_fd, 1);
+            if (rc) return rc;
         }
 
         CHK_ERRNO( libxl_read_exactly(ctx, restore_fd, &hdr,