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+>Writing a New Filesystem</TITLE
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+><DIV
+CLASS="CHAPTER"
+><H1
+><A
+NAME="FILEIO-WRITING">Chapter 29. Writing a New Filesystem</H1
+><P
+>To create a new filesystem it is necessary to define the fstab entry
+and the file IO operations. The easiest way to do this is to copy an
+existing filesystem: either the test filesystem in the FILEIO package,
+or the RAM or ROM filesystem packages.</P
+><P
+>To make this clearer, the following is a brief tour of the FILEIO
+relevant parts of the RAM filesystem.</P
+><P
+>First, it is necessary to provide forward definitions of the functions
+that constitute the filesystem interface:</P
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="PROGRAMLISTING"
+>//==========================================================================
+// Forward definitions
+
+// Filesystem operations
+static int ramfs_mount ( cyg_fstab_entry *fste, cyg_mtab_entry *mte );
+static int ramfs_umount ( cyg_mtab_entry *mte );
+static int ramfs_open ( cyg_mtab_entry *mte, cyg_dir dir, const char *name,
+ int mode, cyg_file *fte );
+static int ramfs_unlink ( cyg_mtab_entry *mte, cyg_dir dir, const char *name );
+static int ramfs_mkdir ( cyg_mtab_entry *mte, cyg_dir dir, const char *name );
+static int ramfs_rmdir ( cyg_mtab_entry *mte, cyg_dir dir, const char *name );
+static int ramfs_rename ( cyg_mtab_entry *mte, cyg_dir dir1, const char *name1,
+ cyg_dir dir2, const char *name2 );
+static int ramfs_link ( cyg_mtab_entry *mte, cyg_dir dir1, const char *name1,
+ cyg_dir dir2, const char *name2, int type );
+static int ramfs_opendir ( cyg_mtab_entry *mte, cyg_dir dir, const char *name,
+ cyg_file *fte );
+static int ramfs_chdir ( cyg_mtab_entry *mte, cyg_dir dir, const char *name,
+ cyg_dir *dir_out );
+static int ramfs_stat ( cyg_mtab_entry *mte, cyg_dir dir, const char *name,
+ struct stat *buf);
+static int ramfs_getinfo ( cyg_mtab_entry *mte, cyg_dir dir, const char *name,
+ int key, void *buf, int len );
+static int ramfs_setinfo ( cyg_mtab_entry *mte, cyg_dir dir, const char *name,
+ int key, void *buf, int len );
+
+// File operations
+static int ramfs_fo_read (struct CYG_FILE_TAG *fp, struct CYG_UIO_TAG *uio);
+static int ramfs_fo_write (struct CYG_FILE_TAG *fp, struct CYG_UIO_TAG *uio);
+static int ramfs_fo_lseek (struct CYG_FILE_TAG *fp, off_t *pos, int whence );
+static int ramfs_fo_ioctl (struct CYG_FILE_TAG *fp, CYG_ADDRWORD com,
+ CYG_ADDRWORD data);
+static int ramfs_fo_fsync (struct CYG_FILE_TAG *fp, int mode );
+static int ramfs_fo_close (struct CYG_FILE_TAG *fp);
+static int ramfs_fo_fstat (struct CYG_FILE_TAG *fp, struct stat *buf );
+static int ramfs_fo_getinfo (struct CYG_FILE_TAG *fp, int key, void *buf, int len );
+static int ramfs_fo_setinfo (struct CYG_FILE_TAG *fp, int key, void *buf, int len );
+
+// Directory operations
+static int ramfs_fo_dirread (struct CYG_FILE_TAG *fp, struct CYG_UIO_TAG *uio);
+static int ramfs_fo_dirlseek (struct CYG_FILE_TAG *fp, off_t *pos, int whence );</PRE
+></TD
+></TR
+></TABLE
+><P
+>We define all of the fstab entries and all of the file IO
+operations. We also define alternatives for the
+<TT
+CLASS="STRUCTFIELD"
+><I
+>fo_read</I
+></TT
+> and
+<TT
+CLASS="STRUCTFIELD"
+><I
+>fo_lseek</I
+></TT
+> file IO operations.</P
+><P
+>We can now define the filesystem table entry. There is a macro,
+<TT
+CLASS="LITERAL"
+>FSTAB_ENTRY</TT
+> to do this:</P
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="PROGRAMLISTING"
+>//==========================================================================
+// Filesystem table entries
+
+// -------------------------------------------------------------------------
+// Fstab entry.
+// This defines the entry in the filesystem table.
+// For simplicity we use _FILESYSTEM synchronization for all accesses since
+// we should never block in any filesystem operations.
+
+FSTAB_ENTRY( ramfs_fste, "ramfs", 0,
+ CYG_SYNCMODE_FILE_FILESYSTEM|CYG_SYNCMODE_IO_FILESYSTEM,
+ ramfs_mount,
+ ramfs_umount,
+ ramfs_open,
+ ramfs_unlink,
+ ramfs_mkdir,
+ ramfs_rmdir,
+ ramfs_rename,
+ ramfs_link,
+ ramfs_opendir,
+ ramfs_chdir,
+ ramfs_stat,
+ ramfs_getinfo,
+ ramfs_setinfo);</PRE
+></TD
+></TR
+></TABLE
+><P
+>The first argument to this macro gives the fstab entry a name, the
+remainder are initializers for the field of the structure.</P
+><P
+>We must also define the file operations table that is installed in all
+open file table entries:</P
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="PROGRAMLISTING"
+>// -------------------------------------------------------------------------
+// File operations.
+// This set of file operations are used for normal open files.
+
+static cyg_fileops ramfs_fileops =
+{
+ ramfs_fo_read,
+ ramfs_fo_write,
+ ramfs_fo_lseek,
+ ramfs_fo_ioctl,
+ cyg_fileio_seltrue,
+ ramfs_fo_fsync,
+ ramfs_fo_close,
+ ramfs_fo_fstat,
+ ramfs_fo_getinfo,
+ ramfs_fo_setinfo
+};</PRE
+></TD
+></TR
+></TABLE
+><P
+>These all point to functions supplied by the filesystem except the
+<TT
+CLASS="STRUCTFIELD"
+><I
+>fo_select</I
+></TT
+> field which is filled with a
+pointer to <TT
+CLASS="FUNCTION"
+>cyg_fileio_seltrue()</TT
+>. This is provided
+by the FILEIO package and is a select function that always returns
+true to all operations.</P
+><P
+>Finally, we need to define a set of file operations for use when
+reading directories. This table only defines the
+<TT
+CLASS="STRUCTFIELD"
+><I
+>fo_read</I
+></TT
+> and
+<TT
+CLASS="STRUCTFIELD"
+><I
+>fo_lseek</I
+></TT
+> operations. The rest are filled
+with stub functions supplied by the FILEIO package that just return an
+error code.</P
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="PROGRAMLISTING"
+>// -------------------------------------------------------------------------
+// Directory file operations.
+// This set of operations are used for open directories. Most entries
+// point to error-returning stub functions. Only the read, lseek and
+// close entries are functional.
+
+static cyg_fileops ramfs_dirops =
+{
+ ramfs_fo_dirread,
+ (cyg_fileop_write *)cyg_fileio_enosys,
+ ramfs_fo_dirlseek,
+ (cyg_fileop_ioctl *)cyg_fileio_enosys,
+ cyg_fileio_seltrue,
+ (cyg_fileop_fsync *)cyg_fileio_enosys,
+ ramfs_fo_close,
+ (cyg_fileop_fstat *)cyg_fileio_enosys,
+ (cyg_fileop_getinfo *)cyg_fileio_enosys,
+ (cyg_fileop_setinfo *)cyg_fileio_enosys
+};</PRE
+></TD
+></TR
+></TABLE
+><P
+>If the filesystem wants to have an instance automatically mounted on
+system startup, it must also define a mount table entry. This is done
+with the <TT
+CLASS="LITERAL"
+>MTAB_ENTRY</TT
+> macro. This is an example from
+the test filesystem of how this is used:</P
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="PROGRAMLISTING"
+>MTAB_ENTRY( testfs_mte1,
+ "/",
+ "testfs",
+ "",
+ 0);</PRE
+></TD
+></TR
+></TABLE
+><P
+>The first argument provides a name for the table entry. The following
+arguments provide initialization for the
+<TT
+CLASS="STRUCTFIELD"
+><I
+>name</I
+></TT
+>, <TT
+CLASS="STRUCTFIELD"
+><I
+>fsname</I
+></TT
+>,
+<TT
+CLASS="STRUCTFIELD"
+><I
+>devname</I
+></TT
+> and <TT
+CLASS="STRUCTFIELD"
+><I
+>data</I
+></TT
+>
+fields respectively.</P
+><P
+>These definitions are adequate to let the new filesystem interact
+with the FILEIO package. The new filesystem now needs to be fleshed
+out with implementations of the functions defined above. Obviously,
+the exact form this takes will depend on what the filesystem is
+intended to do. Take a look at the RAM and ROM filesystems for
+examples of how this has been done.</P
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