URL
https://opencores.org/ocsvn/openrisc/openrisc/trunk
Subversion Repositories openrisc
[/] [openrisc/] [trunk/] [rtos/] [ecos-2.0/] [doc/] [html/] [ref/] [fileio-mount-table.html] - Rev 611
Go to most recent revision | Compare with Previous | Blame | View Log
<!-- Copyright (C) 2003 Red Hat, Inc. --> <!-- This material may be distributed only subject to the terms --> <!-- and conditions set forth in the Open Publication License, v1.0 --> <!-- or later (the latest version is presently available at --> <!-- http://www.opencontent.org/openpub/). --> <!-- Distribution of the work or derivative of the work in any --> <!-- standard (paper) book form is prohibited unless prior --> <!-- permission is obtained from the copyright holder. --> <HTML ><HEAD ><TITLE >Mount Table</TITLE ><meta name="MSSmartTagsPreventParsing" content="TRUE"> <META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+ "><LINK REL="HOME" TITLE="eCos Reference Manual" HREF="ecos-ref.html"><LINK REL="UP" TITLE="File System Support Infrastructure" HREF="fileio.html"><LINK REL="PREVIOUS" TITLE="File System Table" HREF="fileio-fstab.html"><LINK REL="NEXT" TITLE="File Table" HREF="fileio-file-table.html"></HEAD ><BODY CLASS="CHAPTER" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >eCos Reference Manual</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="fileio-fstab.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="fileio-file-table.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="CHAPTER" ><H1 ><A NAME="FILEIO-MOUNT-TABLE">Chapter 21. Mount Table</H1 ><P >The mount table records the filesystems that are actually active. These can be seen as being analogous to mount points in Unix systems.</P ><P >There are two sources of mount table entries. Filesystems (or other components) may export static entries to the table using the <TT CLASS="LITERAL" >MTAB_ENTRY()</TT > macro. Alternatively, new entries may be installed at run time using the <TT CLASS="FUNCTION" >mount()</TT > function. Both types of entry may be unmounted with the <TT CLASS="FUNCTION" >umount()</TT > function.</P ><P >A mount table entry has the following structure:</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >struct cyg_mtab_entry { const char *name; // name of mount point const char *fsname; // name of implementing filesystem const char *devname; // name of hardware device CYG_ADDRWORD data; // private data value cyg_bool valid; // Valid entry? cyg_fstab_entry *fs; // pointer to fstab entry cyg_dir root; // root directory pointer };</PRE ></TD ></TR ></TABLE ><P >The <TT CLASS="STRUCTFIELD" ><I >name</I ></TT > field identifies the mount point. This is used to direct rooted filenames (filenames that begin with "/") to the correct filesystem. When a file name that begins with "/" is submitted, it is matched against the <TT CLASS="STRUCTFIELD" ><I >name</I ></TT > fields of all valid mount table entries. The entry that yields the longest match terminating before a "/", or end of string, wins and the appropriate function from the filesystem table entry is then passed the remainder of the file name together with a pointer to the table entry and the value of the <TT CLASS="STRUCTFIELD" ><I >root</I ></TT > field as the directory pointer.</P ><P >For example, consider a mount table that contains the following entries:</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" > { "/", "msdos", "/dev/hd0", ... } { "/fd", "msdos", "/dev/fd0", ... } { "/rom", "romfs", "", ... } { "/tmp", "ramfs", "", ... } { "/dev", "devfs", "", ... }</PRE ></TD ></TR ></TABLE ><P >An attempt to open "/tmp/foo" would be directed to the RAM filesystem while an open of "/bar/bundy" would be directed to the hard disc MSDOS filesystem. Opening "/dev/tty0" would be directed to the device management filesystem for lookup in the device table.</P ><P >Unrooted file names (those that do not begin with a '/') are passed straight to the filesystem that contains the current directory. The current directory is represented by a pair consisting of a mount table entry and a directory pointer.</P ><P >The <TT CLASS="STRUCTFIELD" ><I >fsname</I ></TT > field points to a string that should match the <TT CLASS="STRUCTFIELD" ><I >name</I ></TT > field of the implementing filesystem. During initialization the mount table is scanned and the <TT CLASS="STRUCTFIELD" ><I >fsname</I ></TT > entries looked up in the filesystem table. For each match, the filesystem's _mount_ function is called and if successful the mount table entry is marked as valid and the <TT CLASS="STRUCTFIELD" ><I >fs</I ></TT > pointer installed.</P ><P >The <TT CLASS="STRUCTFIELD" ><I >devname</I ></TT > field contains the name of the device that this filesystem is to use. This may match an entry in the device table (see later) or may be a string that is specific to the filesystem if it has its own internal device drivers.</P ><P >The <TT CLASS="STRUCTFIELD" ><I >data</I ></TT > field is a private data value. This may be installed either statically when the table entry is defined, or may be installed during the <TT CLASS="FUNCTION" >mount()</TT > operation.</P ><P >The <TT CLASS="STRUCTFIELD" ><I >valid</I ></TT > field indicates whether this mount point has actually been mounted successfully. Entries with a false <TT CLASS="STRUCTFIELD" ><I >valid</I ></TT > field are ignored when searching for a name match.</P ><P >The <TT CLASS="STRUCTFIELD" ><I >fs</I ></TT > field is installed after a successful <TT CLASS="FUNCTION" >mount()</TT > operation to point to the implementing filesystem.</P ><P >The <TT CLASS="STRUCTFIELD" ><I >root</I ></TT > field contains a directory pointer value that the filesystem can interpret as the root of its directory tree. This is passed as the <TT CLASS="PARAMETER" ><I >dir</I ></TT > argument of filesystem functions that operate on rooted filenames. This field must be initialized by the filesystem's <TT CLASS="FUNCTION" >mount()</TT > function.</P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="fileio-fstab.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="ecos-ref.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="fileio-file-table.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >File System Table</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="fileio.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >File Table</TD ></TR ></TABLE ></DIV ></BODY ></HTML >
Go to most recent revision | Compare with Previous | Blame | View Log