7060790: (fs) FileSystem.newWatchService error message confusing when maximum inotify descriptors reached

[Alan Bateman]

This is a minor tweak to the WatchService implementation on Linux so 
that it prints a more useful message in the event that the system is out 
of inotify instances. The errno when inotify_init fails in this case is 
EMFILE and so the IOException is thrown with "Too many open files" which 
can be confused with running out of file descriptors. The patch simple 
translates this error into a more useful message to aid diagnosing the 
issue. I don't propose to include a test with this as tests that check 
exception message tend to be too fragile.

Thanks,
Alan.


diff --git a/src/solaris/classes/sun/nio/fs/LinuxWatchService.java 
b/src/solaris/classes/sun/nio/fs/LinuxWatchService.java
--- a/src/solaris/classes/sun/nio/fs/LinuxWatchService.java
+++ b/src/solaris/classes/sun/nio/fs/LinuxWatchService.java
@@ -58,7 +58,10 @@ class LinuxWatchService
         try {
             ifd = inotifyInit();
         } catch (UnixException x) {
-            throw new IOException(x.errorString());
+            String msg = (x.errno() == EMFILE) ?
+                "User limit of inotify instances reached or too many 
open files" :
+                x.errorString();
+            throw new IOException(msg);
         }
 
         // configure inotify to be non-blocking
diff --git a/src/solaris/native/sun/nio/fs/genUnixConstants.c 
b/src/solaris/native/sun/nio/fs/genUnixConstants.c
--- a/src/solaris/native/sun/nio/fs/genUnixConstants.c
+++ b/src/solaris/native/sun/nio/fs/genUnixConstants.c
@@ -108,6 +108,7 @@ int main(int argc, const char* argv[]) {
     DEF(EROFS);
     DEF(ENODATA);
     DEF(ERANGE);
+    DEF(EMFILE);
 
     // flags used with openat/unlinkat/etc.
 #if defined(AT_SYMLINK_NOFOLLOW) && defined(AT_REMOVEDIR)