fixed(?) ftpfs cache patch

fixed(?) ftpfs cache patch

[mycroftiv]

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Last patch was junk. Changes:
* Only exempt directories from caching, static file transfers require it
* Change -h flag to -c
* Don't interfere with caching of top VM and VMS directories
* Remove redundancy

Thanks cinap for pointing out the problems.
-mycroftiv

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--- /sys/src/cmd/ip/ftpfs/ftpfs.c	Sat Dec 31 17:31:22 2016
+++ ftpfs.c	Tue Feb 13 16:02:46 2018
@@ -85,6 +85,7 @@
 
 char *nosuchfile = "file does not exist";
 char *keyspec = "";
+int docache = 0;
 
 void
 usage(void)
@@ -149,6 +150,9 @@
 	case 'q':
 		quiet = 1;
 		break;
+	case 'c':
+		docache = 1;
+		break;
 	} ARGEND
 	if(argc != 1)
 		usage();
@@ -464,7 +468,8 @@
 				if(readfile(f->node) < 0)
 					return errstring;
 			}
-			CACHED(f->node);
+			if(docache || ((f->node->d->qid.type & QTDIR) == 0))
+				CACHED(f->node);
 		}
 	}
 
@@ -537,7 +542,8 @@
 		if(!ISCACHED(f->node))
 			if(readfile(f->node) < 0)
 				return errstring;
-		CACHED(f->node);
+		if(docache || ((f->node->d->qid.type & QTDIR) == 0))
+			CACHED(f->node);
 		rv = fileread(f->node, (char*)mbuf, off, cnt);
 		if(rv < 0)
 			return errstring;
@@ -617,7 +623,8 @@
 	if(!ISCACHED(p)){
 		invalidate(p);
 		readdir(p);
-		CACHED(p);
+		if(docache || ((f->node->d->qid.type & QTDIR) == 0))
+			CACHED(p);
 	}
 	if(!ISVALID(f->node))
 		return nosuchfile;

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--- /sys/man/4/ftpfs	Tue Jan 17 18:13:59 2012
+++ ftpfs.man	Tue Feb 13 16:36:05 2018
@@ -4,7 +4,7 @@
 .SH SYNOPSIS
 .B ftpfs
 [
-.B -/dqnt
+.B -/dqntc
 ]
 [
 .B -m
@@ -90,6 +90,10 @@
 To see all messages from the server use option
 .BR -d .
 .PP
+By default ftpfs does not cache directories from the remote server. The
+.BR -c
+flag enables directory caching, but this may result in an outdated view of remote files available.
+.PP
 Some systems will hangup an ftp connection that has no activity
 for a given period.  The
 .BR -K
@@ -183,13 +187,9 @@
 However, walking to any valid directory on that machine will succeed
 and cause that directory entry to appear under the mount point.
 .PP
-.I Ftpfs
-caches files and directories.  A directory will fall from the cache
-after 5 quiescent minutes or if the local user changes the
-directory by writing or removing a file.
-Otherwise, remote
+If caching is active, remote
 changes to the directory that occur after the directory has
-been cached might not be immediately visible.
+been cached will not be visible.
 Attempting to walk to
 .IB directory /.flush.ftpfs
 will flush