virtio-9p: fix build on !CONFIG_UTIMENSAT

This patch introduce a fallback mechanism for old systems that do not
support utimensat().  This fix build failure with following warnings:

hw/virtio-9p-local.c: In function 'local_utimensat':
hw/virtio-9p-local.c:479: warning: implicit declaration of function 'utimensat'
hw/virtio-9p-local.c:479: warning: nested extern declaration of 'utimensat'

and:

hw/virtio-9p.c: In function 'v9fs_setattr_post_chmod':
hw/virtio-9p.c:1410: error: 'UTIME_NOW' undeclared (first use in this function)
hw/virtio-9p.c:1410: error: (Each undeclared identifier is reported only once
hw/virtio-9p.c:1410: error: for each function it appears in.)
hw/virtio-9p.c:1413: error: 'UTIME_OMIT' undeclared (first use in this function)
hw/virtio-9p.c: In function 'v9fs_wstat_post_chmod':
hw/virtio-9p.c:2905: error: 'UTIME_OMIT' undeclared (first use in this function)

[NOTE: At this time virtio-9p is only user of utimensat(), and is available
       only when host is linux and CONFIG_VIRTFS is defined.  So there are
       no similar warning for win32.  Please provide a wrapper for win32 in
       oslib-win32.c if new user really requires it.]

v5:
  - Allow fallback on runtime
  - Move qemu_utimensat() to oslib-posix.c
  - Rebased on latest qemu.git
v4:
  - Use tv_now.tv_usec
v3:
  - Use better alternative handling for UTIME_NOW/OMIT
  - Move qemu_utimensat() to cutils.c
V2:
  - Introduce qemu_utimensat()

Acked-by: Chris Wright <chrisw@sous-sol.org>
Acked-by: M. Mohan Kumar <mohan@in.ibm.com>
Acked-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>

hw/virtio-9p-local.c

@@ -480,9 +480,9 @@ static int local_chown(FsContext *fs_ctx, const char *path, FsCred *credp)
 }
 
 static int local_utimensat(FsContext *s, const char *path,
-		       const struct timespec *buf)
+                           const struct timespec *buf)
 {
-    return utimensat(AT_FDCWD, rpath(s, path), buf, AT_SYMLINK_NOFOLLOW);
+    return qemu_utimensat(AT_FDCWD, rpath(s, path), buf, AT_SYMLINK_NOFOLLOW);
 }
 
 static int local_remove(FsContext *ctx, const char *path)

oslib-posix.c

@@ -107,3 +107,51 @@ int qemu_pipe(int pipefd[2])
 
     return ret;
 }
+
+int qemu_utimensat(int dirfd, const char *path, const struct timespec *times,
+                   int flags)
+{
+    struct timeval tv[2], tv_now;
+    struct stat st;
+    int i;
+#ifdef CONFIG_UTIMENSAT
+    int ret;
+
+    ret = utimensat(dirfd, path, times, flags);
+    if (ret != -1 || errno != ENOSYS) {
+        return ret;
+    }
+#endif
+    /* Fallback: use utimes() instead of utimensat() */
+
+    /* happy if special cases */
+    if (times[0].tv_nsec == UTIME_OMIT && times[1].tv_nsec == UTIME_OMIT) {
+        return 0;
+    }
+    if (times[0].tv_nsec == UTIME_NOW && times[1].tv_nsec == UTIME_NOW) {
+        return utimes(path, NULL);
+    }
+
+    /* prepare for hard cases */
+    if (times[0].tv_nsec == UTIME_NOW || times[1].tv_nsec == UTIME_NOW) {
+        gettimeofday(&tv_now, NULL);
+    }
+    if (times[0].tv_nsec == UTIME_OMIT || times[1].tv_nsec == UTIME_OMIT) {
+        stat(path, &st);
+    }
+
+    for (i = 0; i < 2; i++) {
+        if (times[i].tv_nsec == UTIME_NOW) {
+            tv[i].tv_sec = tv_now.tv_sec;
+            tv[i].tv_usec = tv_now.tv_usec;
+        } else if (times[i].tv_nsec == UTIME_OMIT) {
+            tv[i].tv_sec = (i == 0) ? st.st_atime : st.st_mtime;
+            tv[i].tv_usec = 0;
+        } else {
+            tv[i].tv_sec = times[i].tv_sec;
+            tv[i].tv_usec = times[i].tv_nsec / 1000;
+        }
+    }
+
+    return utimes(path, &tv[0]);
+}

qemu-os-posix.h

@@ -39,4 +39,16 @@ void os_setup_post(void);
 typedef struct timeval qemu_timeval;
 #define qemu_gettimeofday(tp) gettimeofday(tp, NULL)
 
+#ifndef CONFIG_UTIMENSAT
+#ifndef UTIME_NOW
+# define UTIME_NOW     ((1l << 30) - 1l)
+#endif
+#ifndef UTIME_OMIT
+# define UTIME_OMIT    ((1l << 30) - 2l)
+#endif
+#endif
+typedef struct timespec qemu_timespec;
+int qemu_utimensat(int dirfd, const char *path, const qemu_timespec *times,
+    int flags);
+
 #endif