/[fuse.before_github]/perl-llin/examples/filter_attr_fs.pl
This is repository of my old source code which isn't updated any more. Go to git.rot13.org for current projects!
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Annotation of /perl-llin/examples/filter_attr_fs.pl

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Revision 116 - (hide annotations)
Thu Dec 6 10:58:07 2007 UTC (16 years, 4 months ago) by dpavlin
File MIME type: text/plain
File size: 6378 byte(s) 
Added contributed filesystem described in e-mail message below:

From: Reuben Thomas <rrt@sc3d.org>
To: dpavlin@rot13.org
Subject: Contribution of sample FS to Fuse

Hi,

I'm just putting the finishing touches to an FS I wrote with Fuse, which
was invaluable, as I couldn't contemplate writing it in C (it's just not
important enough for that much pain!).

I've called it filter_attr_t.pl. It is just loopback_t.pl, augmented with a
function and a little logic so that only files that possess extended
attribute given at mount time are visible. Further, if you try to write to
a file that exists but is not tagged (and hence invisible), you get
-EEXIST, and if you try to unlink a tagged file, it is merely untagged
rather than actually unlinked.

My use for this is to use the backup program Unison, which synchronises two
directory trees, to synch my PDA and my home directory, while excluding
most of the files in my home dir (which would simply not fit in my PDA's
16Mb of file space!). I was amazed to find I couldn't see a FUSE fs which
would do this already, and I was nearly in despair when I remembered Fuse,
and, sure enough, it looked a lot easier than writing a FUSE fs in C.

Of course, the example code was also invaluable, as without it I would have
taken much longer to write the code, and I wouldn't have known some of the
traps.

So, a big thank you, and I attach the current version.

--
http://rrt.sc3d.org/ | Slow Pedestrian Crossing (Anon)
1 dpavlin 116 #!/usr/bin/perl -w
2     # filter_attr_t.pl
3     # Loopback fs that shows only files with a particular xattr
4    
5     # Reuben Thomas 29th November 2007, based on example code from Fuse package
6    
7     use strict;
8     #use blib;
9    
10     use Fuse;
11     use File::ExtAttr ':all';
12     use IO::File;
13     use POSIX qw(ENOENT ENOSYS EEXIST EPERM O_RDONLY O_RDWR O_APPEND O_CREAT O_ACCMODE);
14     use Fcntl qw(S_ISBLK S_ISCHR S_ISFIFO SEEK_SET);
15    
16     # Debug flag
17     #my $debug = 1;
18    
19     # Global settings
20     my ($tag, $real_root, $mountpoint);
21    
22    
23     sub debug {
24     print STDERR shift if $debug;
25     }
26    
27     my $can_syscall = eval {
28     require 'syscall.ph'; # for SYS_mknod and SYS_lchown
29     };
30    
31     if (!$can_syscall && open my $fh, '<', '/usr/include/sys/syscall.h') {
32     my %sys = do { local $/ = undef;
33     <$fh> =~ m/\#define \s+ (\w+) \s+ (\d+)/gxms;
34     };
35     close $fh;
36     if ($sys{SYS_mknod} && $sys{SYS_lchown}) {
37     *SYS_mknod = sub { $sys{SYS_mknod} };
38     *SYS_lchown = sub { $sys{SYS_lchown} };
39     $can_syscall = 1;
40     }
41     }
42    
43     sub tagged {
44     my ($file) = @_;
45     $file =~ s|/$||;
46     my $ret = getfattr($file, $tag);
47     debug("tagged: $file $tag " . defined($ret) . "\n");
48     return $ret;
49     }
50    
51     sub tag {
52     return setfattr(shift, $tag, "");
53     }
54    
55     sub detag {
56     return delfattr(shift, $tag);
57     }
58    
59     sub append_root {
60     return $real_root . shift;
61     }
62    
63     sub err {
64     my ($err) = @_;
65     return $err ? 0 : -$!;
66     }
67    
68     sub x_getattr {
69     debug("x_getattr ");
70     my ($file) = append_root(shift);
71     return -ENOENT() unless tagged($file);
72     my (@list) = lstat($file);
73     return -$! unless @list;
74     return @list;
75     }
76    
77     sub x_readlink {
78     debug("x_readlink ");
79     return readlink(append_root(shift));
80     }
81    
82     sub x_getdir {
83     debug("x_getdir ");
84     my ($dirname) = append_root(shift);
85     return -ENOENT() unless tagged($dirname) && opendir(DIRHANDLE, $dirname);
86     my (@files) = readdir(DIRHANDLE);
87     closedir(DIRHANDLE);
88     my @psifiles = grep {tagged("$dirname/$_")} @files;
89     return (@psifiles, 0);
90     }
91    
92     sub x_mknod {
93     my ($file, $modes, $dev) = @_;
94     return -ENOSYS() if !$can_syscall;
95     debug("x_mknod ");
96     $file = append_root($file);
97     return -EEXIST() if -e $file && !tagged($file);
98     $! = 0;
99     syscall(&SYS_mknod, $file, $modes, $dev);
100     tag($file) if $! == 0;
101     return -$!;
102     }
103    
104     sub x_mkdir {
105     debug("x_mkdir ");
106     my ($name, $perm) = @_;
107     $name = append_root($name);
108     return err(mkdir($name, $perm));
109     }
110    
111     sub x_open {
112     my ($file) = append_root(shift);
113     my ($mode) = shift;
114     my $accmode = $mode & O_ACCMODE;
115     debug("x_open $accmode " . O_ACCMODE . " " . O_WRONLY . " " . O_RDWR . " ");
116     if ($accmode == O_WRONLY || $accmode == O_RDWR) {
117     return -EEXIST() if -e $file && !tagged($file);
118     } else {
119     return -ENOENT() unless tagged($file);
120     }
121     return -$! unless sysopen(FILE, $file, $mode);
122     close(FILE);
123     return 0;
124     }
125    
126     sub x_read {
127     debug("x_read ");
128     my ($file, $bufsize, $off) = @_;
129     my ($rv) = -ENOSYS();
130     my ($handle) = new IO::File;
131     $file = append_root($file);
132     return -ENOENT() unless tagged($file);
133     my ($fsize) = -s $file;
134     return -ENOSYS() unless open($handle, $file);
135     if(seek($handle, $off, SEEK_SET)) {
136     read($handle, $rv, $bufsize);
137     }
138     return $rv;
139     }
140    
141     sub x_write {
142     debug("x_write ");
143     my ($file, $buf, $off) = @_;
144     my ($rv);
145     $file = append_root($file);
146     return -ENOENT() unless tagged($file);
147     my ($fsize) = -s $file;
148     return -ENOSYS() unless open(FILE, '+<', $file);
149     if ($rv = seek(FILE, $off, SEEK_SET)) {
150     $rv = print(FILE $buf);
151     }
152     $rv = -ENOSYS() unless $rv;
153     close(FILE);
154     return length($buf);
155     }
156    
157     sub x_unlink {
158     debug("x_unlink ");
159     my ($file) = append_root(shift);
160     return -ENOENT() unless tagged($file);
161     return err(detag($file));
162     }
163    
164     sub x_symlink {
165     debug("x_symlink ");
166     my ($old) = shift;
167     my ($new) = append_root(shift);
168     return -EEXIST() if -e $new && !tagged($new);
169     return err(symlink($old, $new));
170     }
171    
172     sub x_rename {
173     debug("x_rename ");
174     my ($old) = append_root(shift);
175     my ($new) = append_root(shift);
176     return -ENOENT() unless tagged($old);
177     return -EEXIST() unless !-e $new || tagged($new);
178     my ($err) = rename($old, $new) ? 0 : -ENOENT();
179     return $err;
180     }
181    
182     sub x_link {
183     debug("x_link ");
184     my ($old) = append_root(shift);
185     my ($new) = append_root(shift);
186     return -ENOENT() unless tagged($old);
187     return -EEXIST() unless !-e $new || tagged($new);
188     return err(link($old, $new));
189     }
190    
191     sub x_chown {
192     return -ENOSYS() if !$can_syscall;
193     debug("x_chown ");
194     my ($fn) = append_root(shift);
195     return -ENOENT() unless tagged($fn);
196     my ($uid, $gid) = @_;
197     # perl's chown() does not chown symlinks, it chowns the symlink's
198     # target. it fails when the link's target doesn't exist, because
199     # the stat64() syscall fails.
200     # this causes error messages when unpacking symlinks in tarballs.
201     my ($err) = syscall(&SYS_lchown, $fn, $uid, $gid, $fn) ? -$! : 0;
202     return $err;
203     }
204    
205     sub x_chmod {
206     debug("x_chmod ");
207     my ($fn) = append_root(shift);
208     return -ENOENT() unless tagged($fn);
209     my ($mode) = shift;
210     return err(chmod($mode, $fn));
211     }
212    
213     sub x_truncate {
214     debug("x_truncate ");
215     my ($fn) = append_root(shift);
216     return -ENOENT() unless tagged($fn);
217     return err(truncate($fn, shift));
218     }
219    
220     sub x_utime {
221     debug("x_utime ");
222     my ($fn) = append_root($_[0]);
223     return -ENOENT() unless tagged($fn);
224     return err(utime($_[1], $_[2], $fn));
225     }
226    
227     sub x_rmdir {
228     debug("x_rmdir ");
229     my $dir = append_root(shift);
230     return -ENOENT() unless tagged($dir);
231     return err(detag($dir));
232     }
233    
234     sub x_statfs {
235     debug("x_statfs\n");
236     my $name = append_root(shift);
237     my($bsize, $frsize, $blocks, $bfree, $bavail,
238     $files, $ffree, $favail, $fsid, $basetype, $flag,
239     $namemax, $fstr) = statvfs($real_root) || return -$!;
240     return ($namemax, $files, $ffree, $blocks, $bavail, $bsize);
241     }
242    
243     # If you run the script directly, it will run fusermount, which will in turn
244     # re-run this script. Hence the funky semantics.
245    
246     # Parse command-line arguments
247     $mountpoint = "";
248     if (@ARGV) {
249     $tag = shift(@ARGV);
250     $real_root = shift(@ARGV);
251     $mountpoint = shift(@ARGV);
252     }
253    
254     # Start up FUSE
255     Fuse::main(
256     mountpoint=>$mountpoint,
257     # debug => 1,
258     getattr =>"main::x_getattr",
259     readlink=>"main::x_readlink",
260     getdir =>"main::x_getdir",
261     mknod =>"main::x_mknod",
262     mkdir =>"main::x_mkdir",
263     unlink =>"main::x_unlink",
264     rmdir =>"main::x_rmdir",
265     symlink =>"main::x_symlink",
266     rename =>"main::x_rename",
267     link =>"main::x_link",
268     chmod =>"main::x_chmod",
269     chown =>"main::x_chown",
270     truncate=>"main::x_truncate",
271     utime =>"main::x_utime",
272     open =>"main::x_open",
273     read =>"main::x_read",
274     write =>"main::x_write",
275     statfs =>"main::x_statfs",
276     );

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