Implement $probe_only for the media access modules. sysinstall(8) was

allowed to ignore the probe_only argument of its member functions solely
because in the C language, the file accessor methods open and return a file
descriptor and reading of the data is optional. In shell, the file accessor
methods return data on stdout and that data should not be ignored (large
files could block execution).

So, we must adhere to the probe_only flags and in some cases (in the case of
FTP, for example) change the `get' strategy to simply test existence and
return an appropriate status.

This was required because the up-coming package management stuff makes heavy
use of the probe_only argument to try different package suffixes. Every
media access module must implement $probe_only for the `get' accessor.

usr.sbin/bsdconfig/share/media/cdrom.subr

@@ -146,8 +146,8 @@ f_media_init_cdrom()
 
 # f_media_get_cdrom $device $file [$probe_only]
 #
-# Returns data from $file on a mounted CDROM device. Similar to cat(1).
-# $probe_only is currently unused by this media type.
+# Returns data from $file on a mounted CDROM device. Similar to cat(1). If
+# $probe_only is present and non-NULL, returns success if $file exists.
 #
 f_media_get_cdrom()
 {
@@ -156,7 +156,7 @@ f_media_get_cdrom()
 	f_dprintf "f_media_get_cdrom: dev=[%s] file=[%s] probe_only=%s" \
 	          "$dev" "$file" "$probe_only"
 
-	f_media_generic_get "$MOUNTPOINT" "$file"
+	f_media_generic_get "$MOUNTPOINT" "$file" "$probe_only"
 }
 
 # f_media_shutdown_cdrom $device

usr.sbin/bsdconfig/share/media/common.subr

@@ -83,16 +83,18 @@ f_media_verify()
 	f_struct device_media || f_media_get_type
 }
 
-# f_media_generic_get $base $file
+# f_media_generic_get $base $file [$probe_only]
 #
-# A generic open which follows a well-known "path" of places to look.
+# A generic open which follows a well-known "path" of places to look. If
+# $probe_only is present and non-NULL, returns success if $file exists.
 # 
 f_media_generic_get()
 {
-	local base="$1" file="$2"
+	local base="$1" file="$2" probe_only="$3"
 
 	local fname=f_media_generic_get
-	f_dprintf "%s: base=[%s] files=[%s]" $fname "$base" "$file"
+	f_dprintf "%s: base=[%s] files=[%s] probe_only=%s" \
+	          $fname "$base" "$file" "$probe_only"
 
 	local rel path
 	f_getvar $VAR_RELNAME rel
@@ -104,10 +106,19 @@ f_media_generic_get()
 	; do
 		if [ -f "$path" -a -r "$path" ]; then
 			f_dprintf "%s: file exists path=[%s]" $fname "$path"
+			[ "$probe_only" ] && return $SUCCESS
 			cat "$path"
 			return
 		fi
 	done
+
+	path="$base/releases/$rel/$file" # Final path to try
+	if [ -f "$path" -a -r "$path" ]; then
+		f_dprintf "%s: file exists path=[%s]" $fname "$path"
+		[ "$probe_only" ] && return $SUCCESS
+	elif [ "$probe_only" ]; then
+		return $FAILURE
+	fi
 	cat "$base/releases/$rel/$file" # Final path to try
 }
 

usr.sbin/bsdconfig/share/media/directory.subr

@@ -117,7 +117,8 @@ f_media_init_directory()
 # f_media_get_directory $device $file [$probe_only]
 #
 # Returns data from $file in the existing/current filesystem. Similar to
-# cat(1). $probe_only is currently unused by this media type.
+# cat(1). If $probe_only is present and non-NULL, returns success if $file
+# exists.
 #
 f_media_get_directory()
 {
@@ -127,7 +128,7 @@ f_media_get_directory()
 	          "$dev" "$file" "$probe_only"
 
 	device_$dev get private path
-	f_media_generic_get "$path" "$file"
+	f_media_generic_get "$path" "$file" "$probe_only"
 }
 
 # f_media_shutdown_directory $device

usr.sbin/bsdconfig/share/media/dos.subr

@@ -125,7 +125,7 @@ f_media_init_dos()
 # f_media_get_dos $device $file [$probe_only]
 #
 # Returns data from $file on a mounted DOS partition device. Similar to cat(1).
-# $probe_only is currently unused by this media type.
+# If $probe_only is present and non-NULL, returns success if $file exists.
 #
 f_media_get_dos()
 {
@@ -134,7 +134,7 @@ f_media_get_dos()
 	f_dprintf "f_media_get_dos: dev=[%s] file=[%s] probe_only=%s" \
 	          "$dev" "$file" "$probe_only"
 
-	f_media_generic_get "$MOUNTPOINT" "$file"
+	f_media_generic_get "$MOUNTPOINT" "$file" "$probe_only"
 }
 
 # f_media_shutdown_dos $device

usr.sbin/bsdconfig/share/media/floppy.subr

@@ -178,6 +178,8 @@ f_media_get_floppy()
 			f_media_init_floppy "$dev" || return $FAILURE
 			nretries=$(( $nretries - 1 ))
 		done
+	elif [ "$probe_only" ]; then
+		return $SUCCESS
 	fi
 	cat "$fp"
 }

usr.sbin/bsdconfig/share/media/ftp.subr

@@ -792,8 +792,8 @@ f_media_init_ftp()
 #
 # Returns data from $file on an FTP server using ftp(1). Please note that
 # $device is unused but must be present (even if null). Information is instead
-# gathered from the environment. $probe_only is currently unused by this media
-# type.
+# gathered from the environment. If $probe_only is present and non-NULL,
+# returns success if $file exists.
 #
 # Variables from variable.subr used to configure the connection are as follows
 # (all of which are configured by f_media_set_ftp above):
@@ -900,6 +900,17 @@ f_media_get_ftp()
 
 	f_dprintf "sending ftp request for: %s" "ftp://$host$port/$dir/$file"
 
+	if [ "$probe_only" ]; then
+		local url="ftp://$userpass$host$port/$dir/$file"
+		[ "$use_anon" ] && url="ftp://$host$port/$dir/$file"
+		if ! size=$( fetch -s "$url" 2>&1 ) || ! f_isinteger "$size"
+		then
+			f_dprintf "request failed! size response=[%s]" "$size"
+			return $FAILURE
+		fi
+		return $SUCCESS
+	fi
+
 	eval FTPMODE=\"\$mode\" ${use_anon:+FTPANONPASS=\"\$pass\"} \
 	     ftp -V ${use_anon:+-a} -o - \
 	     	\"ftp://\$userpass\$host\$port/\$dir/\$file\" 2> /dev/null

usr.sbin/bsdconfig/share/media/nfs.subr

@@ -210,8 +210,8 @@ f_media_init_nfs()
 
 # f_media_get_nfs $device $file [$probe_only]
 #
-# Returns data from $file on a mounted NFS device. Similar to cat(1).
-# $probe_only is currently unused by this media type.
+# Returns data from $file on a mounted NFS device. Similar to cat(1). If
+# $probe_only is present and non-NULL, returns success if $file exists.
 #
 f_media_get_nfs()
 {
@@ -220,7 +220,7 @@ f_media_get_nfs()
 	f_dprintf "f_media_get_nfs: dev=[%s] file=[%s] probe_only=%s" \
 	          "$dev" "$file" "$probe_only"
 
-	f_media_generic_get "$MOUNTPOINT" "$file"
+	f_media_generic_get "$MOUNTPOINT" "$file" "$probe_only"
 }
 
 # f_media_shutdown_nfs $device

usr.sbin/bsdconfig/share/media/ufs.subr

@@ -155,7 +155,7 @@ f_media_init_ufs()
 # f_media_get_ufs $device $file [$probe_only]
 #
 # Returns data from $file on a mounted UFS partition device. Similar to cat(1).
-# $probe_only is currently unused by this media type.
+# If $probe_only is present and non-NULL, returns success if $file exists.
 #
 f_media_get_ufs()
 {
@@ -164,7 +164,7 @@ f_media_get_ufs()
 	f_dprintf "f_media_get_ufs: dev=[%s] file=[%s] probe_only=%s" \
 	          "$dev" "$file" "$probe_only"
 
-	f_media_generic_get "$MOUNTPOINT" "$file"
+	f_media_generic_get "$MOUNTPOINT" "$file" "$probe_only"
 }
 
 # f_media_shutdown_ufs $device

usr.sbin/bsdconfig/share/media/usb.subr

@@ -135,7 +135,7 @@ f_media_init_usb()
 # f_media_get_usb $device $file [$probe_only]
 #
 # Returns data from $file on a mounted USB disk device. Similar to cat(1).
-# $probe_only is currently unused by this media type.
+# If $probe_only is present and non-NULL, returns success if $file exists.
 #
 f_media_get_usb()
 {
@@ -144,7 +144,7 @@ f_media_get_usb()
 	f_dprintf "f_media_get_usb: dev=[%s] file=[%s] probe_only=%s" \
 	          "$dev" "$file" "$probe_only"
 
-	f_media_generic_get "$MOUNTPOINT" "$file"
+	f_media_generic_get "$MOUNTPOINT" "$file" "$probe_only"
 }
 
 # f_media_shutdown_usb $device