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->Writing a New Filesystem</TITLE
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-><DIV
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-><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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