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+>Mount Table</TITLE
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+><DIV
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+><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
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