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><H1
><A
NAME="FILEIO-MOUNTING">Chapter 25. Initialization and Mounting</H1
><P
>As mentioned previously, mount table entries can be sourced from two
places. Static entries may be defined by using the
<TT
CLASS="LITERAL"
>MTAB_ENTRY()</TT
> macro. Such entries will be
automatically mounted on system startup. For each entry in the mount
table that has a non-null <TT
CLASS="STRUCTFIELD"
><I
>name</I
></TT
> field the
filesystem table is searched for a match with the
<TT
CLASS="STRUCTFIELD"
><I
>fsname</I
></TT
> field. If a match is found the
filesystem's <TT
CLASS="STRUCTFIELD"
><I
>mount</I
></TT
> entry is called and if
successful the mount table entry marked valid and the
<TT
CLASS="STRUCTFIELD"
><I
>fs</I
></TT
> field initialized. The
<TT
CLASS="FUNCTION"
>mount()</TT
> function is responsible for initializing
the <TT
CLASS="STRUCTFIELD"
><I
>root</I
></TT
> field.</P
><P
>The size of the mount table is defined by the configuration value
<TT
CLASS="LITERAL"
>CYGNUM_FILEIO_MTAB_MAX</TT
>. Any entries that have not
been statically defined are available for use by dynamic mounts.</P
><P
>A filesystem may be mounted dynamically by calling <TT
CLASS="FUNCTION"
>mount()</TT
>. This
function has the following prototype:</P
><TABLE
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><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>int mount( const char *devname,
const char *dir,
const char *fsname);</PRE
></TD
></TR
></TABLE
><P
>The <TT
CLASS="PARAMETER"
><I
>devname</I
></TT
> argument identifies a device that
will be used by this filesystem and will be assigned to the
<TT
CLASS="STRUCTFIELD"
><I
>devname</I
></TT
> field of the mount table entry.</P
><P
>The <TT
CLASS="PARAMETER"
><I
>dir</I
></TT
> argument is the mount point name, it
will be assigned to the <TT
CLASS="STRUCTFIELD"
><I
>name</I
></TT
> field of the
mount table entry.</P
><P
>The <TT
CLASS="PARAMETER"
><I
>fsname</I
></TT
> argument is the name of the
implementing filesystem, it will be assigned to the
<TT
CLASS="STRUCTFIELD"
><I
>fsname</I
></TT
> entry of the mount table entry.</P
><P
>The process of mounting a filesystem dynamically is as follows. First
a search is made of the mount table for an entry with a NULL
<TT
CLASS="STRUCTFIELD"
><I
>name</I
></TT
> field to be used for the new mount
point. The filesystem table is then searched for an entry whose name
matches <TT
CLASS="STRUCTFIELD"
><I
>fsname</I
></TT
>. If this is successful then
the mount table entry is initialized and the filesystem's
<TT
CLASS="FUNCTION"
>mount()</TT
> operation called. If this is successful,
the mount table entry is marked valid and the
<TT
CLASS="STRUCTFIELD"
><I
>fs</I
></TT
> field initialized.</P
><P
>Unmounting a filesystem is done by the <TT
CLASS="FUNCTION"
>umount()</TT
>
function. This can unmount filesystems whether they were mounted
statically or dynamically.</P
><P
>The <TT
CLASS="FUNCTION"
>umount()</TT
> function has the following prototype:</P
><TABLE
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><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>int umount( const char *name );</PRE
></TD
></TR
></TABLE
><P
>The mount table is searched for a match between the
<TT
CLASS="PARAMETER"
><I
>name</I
></TT
> argument and the entry
<TT
CLASS="STRUCTFIELD"
><I
>name</I
></TT
> field. When a match is found the
filesystem's <TT
CLASS="FUNCTION"
>umount()</TT
> operation is called and if
successful, the mount table entry is invalidated by setting its
<TT
CLASS="STRUCTFIELD"
><I
>valid</I
></TT
> field false and the
<TT
CLASS="STRUCTFIELD"
><I
>name</I
></TT
> field to NULL.</P
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