This patch reintroduces support for extended attributes in Solaris.
It is subtly different from the support in JDK17 and earlier, in that
attributes are implicitly namespaced, like Linux, as the code is now
shared. This means that the 2 native attribute files you normally see
are missing, and all the attribute filenames get a "user." prefix.

--- a/src/java.base/unix/native/libnio/fs/UnixNativeDispatcher.c	Sat Oct 25 15:35:56 2025
+++ b/src/java.base/unix/native/libnio/fs/UnixNativeDispatcher.c	Wed Nov 12 14:16:06 2025
@@ -262,6 +262,106 @@
 #endif
 
 /**
+ * Solaris and illumos do not have the f*xattr set of functions, so
+ * provide a reasonable facsimile here.
+ */
+#ifdef __solaris__
+ssize_t sunos_flistxattr(int fd, char* list, size_t size) {
+  int xfd = openat(fd, ".", O_RDONLY|O_XATTR);
+  DIR *dirp = fdopendir(xfd);
+  int ilist = 0;
+  int ilen = 0;
+  struct dirent *dp;
+  while (dp = readdir(dirp)) {
+    if (strcmp(dp->d_name, ".") && strcmp(dp->d_name, "..")) {
+      ilen = strlen(dp->d_name);
+      if (size == 0) {
+	/*
+	 * size==0 means just return the total size.
+	 */
+	ilist += ilen;
+	ilist += 1;
+      } else {
+	/*
+	 * If the name won't fit, break out and exit
+	 */
+	if (ilist + ilen + 1 > size) {
+	  ilist = -1;
+	  break;
+	}
+	memcpy(list + ilist, dp->d_name, ilen);
+	ilist += ilen;
+	list[ilist] = 0;
+	ilist += 1;
+      }
+    }
+  }
+  closedir(dirp);
+  close(xfd);
+  /*
+   * If the result won't fit, return -1 and set errno to ERANGE
+   */
+  if (ilist == -1)
+    errno = ERANGE;
+  return ilist;
+}
+ssize_t sunos_fgetxattr(int fd, const char* name, void* value, size_t size) {
+  int ifd = dup(fd);
+  int gfd = openat(ifd, ".", O_RDONLY|O_XATTR);
+  int rfd = openat(gfd, name, O_RDONLY);
+  ssize_t nread;
+  int xerr = 0;
+  int nbuf[2];
+  /*
+   * return size of entry and don't do the read if size passed as 0
+   */
+  if (size == 0) {
+    struct stat lbuf;
+    fstat(rfd, &lbuf);
+    nread = (ssize_t) lbuf.st_size;
+  } else {
+    nread = read(rfd, value, size);
+    if (nread > size) {
+      nread = -1;
+      xerr = -1;
+    }
+    /*
+     * now we need to check if there's any more to read, and error
+     * out if there is as the buffer we were given is too small.
+     * if the buffer was exactly the right size this read will return zero
+     */
+    if (nread == size) {
+      if (read(rfd, &nbuf, 2) > 0) {
+	nread = -1;
+	xerr = -1;
+      }
+    }
+  }
+  close(rfd);
+  close(gfd);
+  close(ifd);
+  if (xerr == -1) {
+    errno = ERANGE;
+  }
+  return nread;
+}
+int sunos_fsetxattr(int fd, const char* name, void* value, size_t size) {
+  int xfd = openat(fd, ".", O_RDONLY|O_XATTR);
+  int wfd = openat(xfd, name, O_CREAT|O_RDWR, 0644);
+  int uerr = write(wfd, value, size);
+  close(wfd);
+  close(xfd);
+  return uerr;
+}
+int sunos_fremovexattr(int fd, const char* name) {
+  int xfd = openat(fd, ".", O_RDONLY|O_XATTR);
+  int uerr = unlinkat(xfd, name, 0);
+  close(xfd);
+  return uerr;
+}
+#endif
+
+/**
  * Call this to throw an internal UnixException when a system/library
  * call fails
  */
@@ -1478,6 +1578,8 @@
     res = fgetxattr(fd, name, value, valueLen, 0, 0);
 #elif defined(_AIX)
     res = fgetea(fd, name, value, valueLen);
+#elif defined(__solaris__)
+    res = sunos_fgetxattr(fd, name, value, valueLen);
 #else
     throwUnixException(env, ENOTSUP);
 #endif
@@ -1501,6 +1603,8 @@
     res = fsetxattr(fd, name, value, valueLen, 0, 0);
 #elif defined(_AIX)
     res = fsetea(fd, name, value, valueLen, 0);
+#elif defined(__solaris__)
+    res = sunos_fsetxattr(fd, name, value, valueLen);
 #else
     throwUnixException(env, ENOTSUP);
 #endif
@@ -1522,6 +1626,8 @@
     res = fremovexattr(fd, name, 0);
 #elif defined(_AIX)
     res = fremoveea(fd, name);
+#elif defined(__solaris__)
+    res = sunos_fremovexattr(fd, name);
 #else
     throwUnixException(env, ENOTSUP);
 #endif
@@ -1543,6 +1649,8 @@
     res = flistxattr(fd, list, (size_t)size, 0);
 #elif defined(_AIX)
     res = flistea(fd, list, (size_t)size);
+#elif defined(__solaris__)
+    res = sunos_flistxattr(fd, list, (size_t)size);
 #else
     throwUnixException(env, ENOTSUP);
 #endif