Add option for deny watching of subfiles for certain filesystem types

In many cases (depending on inotify_watch_add() options) libinotify-kqueue
opens all files in watched directory that can be inappropriate on certain
filesystems like network or mtpfs due to large overhead of open() operation.
That is why skip-subfiles configure option is introduced. If this option
was enabled at configure time, libinotify-kqueue checks filesystem type on
inotify_watch_add() invocation and compares with blacklist to deceide
if it necessary to watch for subfiles or not.
That disables notifications of subfiles content or attribute modifications
but still allow to track their creation, deletion and renaming.

E.g: to prohibit of opening subfiles on NFS and MTP-fs(mounted with fuse) use

./configure --enable-skip-subfiles=fusefs,nfs

configure.ac

@@ -409,4 +409,33 @@ AS_IF([test "x$enable_native_semaphores" != "xno"], [
 ])
 
 
+AC_ARG_ENABLE([skip-subfiles],
+    AS_HELP_STRING([--enable-skip-subfiles=fstype@<:@,fstype@:>@], [List of filesystem types where opening of subfiles is not performed]),
+    [
+        AC_CHECK_MEMBER([struct statfs.f_fstypename],
+        [
+            AC_DEFINE([STATFS_HAVE_F_FSTYPENAME],[1],[Define to 1 if struct statfs have f_fstypename field])
+        ],
+        [
+            AC_CHECK_MEMBER([struct statvfs.f_fstypename],
+            [
+                AC_DEFINE([STATVFS_HAVE_F_FSTYPENAME],[1],[Define to 1 if struct statvfs have f_fstypename field])
+            ],
+            [
+                AC_MSG_ERROR(No means for detecting filesystem type found. Remove --enable-skip-subfiles option!)
+            ],
+            [
+                @%:@include <sys/statvfs.h>
+            ])
+        ],
+        [
+            @%:@include <sys/param.h>
+            @%:@include <sys/mount.h>
+        ])
+        subfiles_fs_list=`echo "\"$enable_skip_subfiles\"" | $SED -e 's/,/", "/g'`
+        AC_DEFINE_UNQUOTED([SKIP_SUBFILES],[$subfiles_fs_list],[List of filesystem types where opening of subfiles is not performed])
+    ]
+)
+
+
 AC_OUTPUT

inotify-watch.c

@@ -23,6 +23,12 @@
 #include "compat.h"
 
 #include <sys/types.h>
+#ifdef STATFS_HAVE_F_FSTYPENAME
+#include <sys/mount.h> /* fstatfs */
+#endif
+#ifdef STATVFS_HAVE_F_FSTYPENAME
+#include <sys/statvfs.h> /* fstatvfs */
+#endif
 #include <sys/stat.h>  /* fstat */
 
 #include <assert.h>    /* assert */
@@ -39,6 +45,48 @@
 #include "watch-set.h"
 #include "watch.h"
 
+#ifdef SKIP_SUBFILES
+static const char *skip_fs_types[] = { SKIP_SUBFILES };
+
+/**
+ * Check if watch descriptor belongs a filesystem
+ * where opening of subfiles is inwanted.
+ *
+ * @param[in] fd A file descriptor of a watched entry.
+ * @return 1 if watching for subfiles is unwanted, 0 otherwise.
+ **/
+static int
+iwatch_want_skip_subfiles (int fd)
+{
+#ifdef STATFS_HAVE_F_FSTYPENAME
+    struct statfs st;
+#else
+    struct statvfs st;
+#endif
+    size_t i;
+    int ret;
+
+    memset (&st, 0, sizeof (st));
+#ifdef STATFS_HAVE_F_FSTYPENAME
+    ret = fstatfs (fd, &st);
+#else
+    ret = fstatvfs (fd, &st);
+#endif
+    if (ret == -1) {
+        perror_msg ("fstatfs failed on %d");
+        return 0;
+    }
+
+    for (i = 0; i < nitems (skip_fs_types); i++) {
+        if (strcmp (st.f_fstypename, skip_fs_types[i]) == 0) {
+            return 1;
+        }
+    }
+
+    return 0;
+}
+#endif
+
 /**
  * Preform minimal initialization required for opening watch descriptor
  *
@@ -117,6 +165,9 @@ iwatch_init (worker *wrk, int fd, uint32_t flags)
         closedir (dir);
 #else
         iw->dir = dir;
+#endif
+#ifdef SKIP_SUBFILES
+        iw->skip_subfiles = iwatch_want_skip_subfiles (fd);
 #endif
     }
 
@@ -183,6 +234,12 @@ iwatch_add_subwatch (i_watch *iw, dep_item *di)
         return NULL;
     }
 
+#ifdef SKIP_SUBFILES
+    if (iw->skip_subfiles) {
+        goto lstat;
+    }
+#endif
+
     watch *w = watch_set_find (&iw->watches, di->inode);
     if (w != NULL) {
         di->type = w->flags & S_IFMT;

inotify-watch.h

@@ -40,6 +40,9 @@ struct i_watch {
 #endif
     worker *wrk;               /* pointer to a parent worker structure */
     int is_closed;             /* inotify watch is stopped but not freed yet */
+#ifdef SKIP_SUBFILES
+    int skip_subfiles;         /* Fs is not safe to start subwatches */
+#endif
     uint32_t flags;            /* flags in the inotify format */
     ino_t inode;               /* inode number of watched inode */
     dev_t dev;                 /* device number of watched inode */