+++ /dev/null
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-<HTML
-><HEAD
-><TITLE
->File Table</TITLE
-><meta name="MSSmartTagsPreventParsing" content="TRUE">
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-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="Mount Table"
-HREF="fileio-mount-table.html"><LINK
-REL="NEXT"
-TITLE="Directories"
-HREF="fileio-directories.html"></HEAD
-><BODY
-CLASS="CHAPTER"
-BGCOLOR="#FFFFFF"
-TEXT="#000000"
-LINK="#0000FF"
-VLINK="#840084"
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-><DIV
-CLASS="NAVHEADER"
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-SUMMARY="Header navigation table"
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->eCos Reference Manual</TH
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-><HR
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-WIDTH="100%"></DIV
-><DIV
-CLASS="CHAPTER"
-><H1
-><A
-NAME="FILEIO-FILE-TABLE">Chapter 22. File Table</H1
-><P
->Once a file has been opened it is represented by an open file
-object. These are allocated from an array of available file
-objects. User code accesses these open file objects via a second array
-of pointers which is indexed by small integer offsets. This gives the
-usual Unix file descriptor functionality, complete with the various
-duplication mechanisms.</P
-><P
->A file table entry has the following structure:</P
-><TABLE
-BORDER="5"
-BGCOLOR="#E0E0F0"
-WIDTH="70%"
-><TR
-><TD
-><PRE
-CLASS="PROGRAMLISTING"
->struct CYG_FILE_TAG
-{
- cyg_uint32 f_flag; /* file state */
- cyg_uint16 f_ucount; /* use count */
- cyg_uint16 f_type; /* descriptor type */
- cyg_uint32 f_syncmode; /* synchronization protocol */
- struct CYG_FILEOPS_TAG *f_ops; /* file operations */
- off_t f_offset; /* current offset */
- CYG_ADDRWORD f_data; /* file or socket */
- CYG_ADDRWORD f_xops; /* extra type specific ops */
- cyg_mtab_entry *f_mte; /* mount table entry */
-};</PRE
-></TD
-></TR
-></TABLE
-><P
->The <TT
-CLASS="STRUCTFIELD"
-><I
->f_flag</I
-></TT
-> field contains some FILEIO
-control bits and some bits propagated from the
-<TT
-CLASS="PARAMETER"
-><I
->flags</I
-></TT
-> argument of the
-<TT
-CLASS="FUNCTION"
->open()</TT
-> call (defined by
-<TT
-CLASS="LITERAL"
->CYG_FILE_MODE_MASK</TT
->).</P
-><P
->The <TT
-CLASS="STRUCTFIELD"
-><I
->f_ucount</I
-></TT
-> field contains a use count that
-controls when a file will be closed. Each duplicate in the file
-descriptor array counts for one reference here. It is also
-incremented around each I/O operation to ensure that the file cannot
-be closed while it has current I/O operations.</P
-><P
->The <TT
-CLASS="STRUCTFIELD"
-><I
->f_type</I
-></TT
-> field indicates the type of the
-underlying file object. Some of the possible values here are
-<TT
-CLASS="LITERAL"
->CYG_FILE_TYPE_FILE</TT
->,
-<TT
-CLASS="LITERAL"
->CYG_FILE_TYPE_SOCKET</TT
-> or <TT
-CLASS="LITERAL"
->CYG_FILE_TYPE_DEVICE</TT
->.</P
-><P
->The <TT
-CLASS="STRUCTFIELD"
-><I
->f_syncmode</I
-></TT
-> field is copied from the
-<TT
-CLASS="STRUCTFIELD"
-><I
->syncmode</I
-></TT
-> field of the implementing
-filesystem. Its use is described in <A
-HREF="fileio-synchronization.html"
->Chapter 24</A
->.</P
-><P
->The <TT
-CLASS="STRUCTFIELD"
-><I
->f_offset</I
-></TT
-> field records the current file
-position. It is the responsibility of the file operation functions to
-keep this field up to date.</P
-><P
->The <TT
-CLASS="STRUCTFIELD"
-><I
->f_data</I
-></TT
-> field contains private data
-placed here by the underlying filesystem. Normally this will be a
-pointer to, or handle on, the filesystem object that implements this
-file.</P
-><P
->The <TT
-CLASS="STRUCTFIELD"
-><I
->f_xops</I
-></TT
-> field contains a pointer to any
-extra type specific operation functions. For example, the socket I/O
-system installs a pointer to a table of functions that implement the
-standard socket operations.</P
-><P
->The <TT
-CLASS="STRUCTFIELD"
-><I
->f_mte</I
-></TT
-> field contains a pointer to the
-parent mount table entry for this file. It is used mainly to implement
-the synchronization protocol. This may contain a pointer to some other
-data structure in file objects not derived from a filesystem.</P
-><P
->The <TT
-CLASS="STRUCTFIELD"
-><I
->f_ops</I
-></TT
-> field contains a pointer to a
-table of file I/O operations. This has the following structure:</P
-><TABLE
-BORDER="5"
-BGCOLOR="#E0E0F0"
-WIDTH="70%"
-><TR
-><TD
-><PRE
-CLASS="PROGRAMLISTING"
->struct CYG_FILEOPS_TAG
-{
- int (*fo_read) (struct CYG_FILE_TAG *fp, struct CYG_UIO_TAG *uio);
- int (*fo_write) (struct CYG_FILE_TAG *fp, struct CYG_UIO_TAG *uio);
- int (*fo_lseek) (struct CYG_FILE_TAG *fp, off_t *pos, int whence );
- int (*fo_ioctl) (struct CYG_FILE_TAG *fp, CYG_ADDRWORD com,
- CYG_ADDRWORD data);
- int (*fo_select) (struct CYG_FILE_TAG *fp, int which, CYG_ADDRWORD info);
- int (*fo_fsync) (struct CYG_FILE_TAG *fp, int mode );
- int (*fo_close) (struct CYG_FILE_TAG *fp);
- int (*fo_fstat) (struct CYG_FILE_TAG *fp, struct stat *buf );
- int (*fo_getinfo) (struct CYG_FILE_TAG *fp, int key, char *buf, int len );
- int (*fo_setinfo) (struct CYG_FILE_TAG *fp, int key, char *buf, int len );
-};</PRE
-></TD
-></TR
-></TABLE
-><P
->It should be obvious from the names of most of these functions what
-their responsibilities are. The <TT
-CLASS="FUNCTION"
->fo_getinfo()</TT
->
-and <TT
-CLASS="FUNCTION"
->fo_setinfo()</TT
-> function pointers, like their
-counterparts in the filesystem structure, implement minor control and
-info functions such as <TT
-CLASS="FUNCTION"
->fpathconf()</TT
->.</P
-><P
->The second argument to the <TT
-CLASS="FUNCTION"
->fo_read()</TT
-> and
-<TT
-CLASS="FUNCTION"
->fo_write()</TT
-> function pointers is a pointer to a
-UIO structure:</P
-><TABLE
-BORDER="5"
-BGCOLOR="#E0E0F0"
-WIDTH="70%"
-><TR
-><TD
-><PRE
-CLASS="PROGRAMLISTING"
->struct CYG_UIO_TAG
-{
- struct CYG_IOVEC_TAG *uio_iov; /* pointer to array of iovecs */
- int uio_iovcnt; /* number of iovecs in array */
- off_t uio_offset; /* offset into file this uio corresponds to */
- ssize_t uio_resid; /* residual i/o count */
- enum cyg_uio_seg uio_segflg; /* see above */
- enum cyg_uio_rw uio_rw; /* see above */
-};
-
-struct CYG_IOVEC_TAG
-{
- void *iov_base; /* Base address. */
- ssize_t iov_len; /* Length. */
-};</PRE
-></TD
-></TR
-></TABLE
-><P
->This structure encapsulates the parameters of any data transfer
-operation. It provides support for scatter/gather operations and
-records the progress of any data transfer. It is also compatible with
-the I/O operations of any BSD-derived network stacks and filesystems.</P
-><P
->When a file is opened (or a file object created by some other means,
-such as <TT
-CLASS="FUNCTION"
->socket()</TT
-> or <TT
-CLASS="FUNCTION"
->accept()</TT
->) it is the
-responsibility of the filesystem open operation to initialize all the
-fields of the object except the <TT
-CLASS="STRUCTFIELD"
-><I
->f_ucount</I
-></TT
->,
-<TT
-CLASS="STRUCTFIELD"
-><I
->f_syncmode</I
-></TT
-> and
-<TT
-CLASS="STRUCTFIELD"
-><I
->f_mte</I
-></TT
-> fields. Since the
-<TT
-CLASS="STRUCTFIELD"
-><I
->f_flag</I
-></TT
-> field will already contain bits belonging to the FILEIO
-infrastructure, any changes to it must be made with the appropriate
-logical operations.</P
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