<foil>
<title>Introduction</title>
-<para>Devices are files in /dev</para>
+<para>
+Devices in POSIX Systems are files in /dev directory. As with any files
+in POSIX, they may be opened, closed, read from, written to, seeked,
+ioctl'd, and others.
+</para>
+
+<para>
+Examples of device files:
+</para>
<itemizedlist>
<listitem>
-<para>/dev/sda</para>
+<para>
+/dev/sda - A SCSI block device
+</para>
</listitem>
<listitem>
-<para>/dev/ttyS0</para>
+<para>
+/dev/ttyS0 - A Serial terminal device
+</para>
</listitem>
</itemizedlist>
</foil>
+<foil>
+<title>POSIX I/O calls</title>
+<para>
+POSIX systems have some standard calls for I/O. Since devices are files,
+these same system calls are used to work with devices. We are gonna work
+with the following calls:
+</para>
+<itemizedlist>
+<listitem><para>
+open
+</para></listitem>
+<listitem><para>
+read
+</para></listitem>
+<listitem><para>
+write
+</para></listitem>
+<listitem><para>
+close
+</para></listitem>
+<listitem><para>
+lseek
+</para></listitem>
+<listitem><para>
+ioctl
+</para></listitem>
+</itemizedlist>
+</foil>
+
+<foil>
+<title>open</title>
+<para>
+The open system call opens a file. When working with devices, that's
+when some initialization should be done. Some devices may be opened only
+once at a time.
+</para>
+<para>
+int open (char * filename, int flags);
+</para>
+<para>
+flags may be O\_RDONLY, O\_WRONLY, O\_RDWR and many others, some not
+important for devices.
+</para>
+<para>
+Example:
+</para>
+<para>
+fd = open ("/dev/ttyS0", O\_RDWR);
+</para>
+</foil>
+
+<foil>
+<title>close</title>
+<para>
+The close system call closes an open file.
+</para>
+<para>
+int close (int fd);
+</para>
+<para>
+Example:
+</para>
+<para>
+close (fd);
+</para>
+</foil>
+
+<foil>
+<title>read</title>
+<para>
+The read system call reads data from an open file into a buffer. For
+devices, it reads from the device.
+</para>
+<para>
+int read (int fd, char *buffer, int bsz);
+</para>
+<para>
+Read returns the number of bytes written into the buffer, which may be
+less than the number of bytes requested for any number of reasons.
+</para>
+<para>
+Example:
+</para>
+<para>
+c = read (fd, buffer, sizeof (buffer));
+</para>
+</foil>
+
+<foil>
+<title>write</title>
+<para>
+The write system call writes data to an open file from a buffer. For
+devices, it writes to the device.
+</para>
+<para>
+int write (int fd, char *buffer, int bsz);
+</para>
+<para>
+Write returns the number of bytes written to the file, which may be
+less than the number of bytes requested for any number of reasons.
+</para>
+<para>
+Example:
+</para>
+<para>
+c = write (fd, buffer, strlen (buffer));
+</para>
+</foil>
+
+<foil>
+<title>lseek</title>
+<para>
+The lseek system call changes the current position of the file, allowing
+to read or write in that position. Seeking on a device may have many
+different meanings.
+</para>
+<para>
+off\_t lseek (int fd, off\_t pos, int whence);
+</para>
+<para>
+The meaning of the position depends on the value of whence, which can be
+SEEK\_SET (the absolute position), SEEK\_CUR (relative to the current
+position), SEEK\_END (relative to the end of the file).
+</para>
+<para>
+Example:
+</para>
+<para>
+lseek (fd, 0, SEEK\_END);
+</para>
+</foil>
+
+<foil>
+<title>ioctl</title>
+<para>
+The ioctl system call is a catch-all operation. For those operations
+which doesn't fit in the read/write model, the ioctl allows the user to
+send a command with an optional argument to the device. This command may
+accept input or generate output.
+</para>
+<para>
+int ioctl (int fd, int request, char *arg);
+</para>
+<para>
+The last argument is optional and depends on the type of request. Every
+device or device class may have its different set of ioctl's.
+</para>
+<para>
+Example:
+</para>
+<para>
+struct ifreq req; ioctl (fd, SIOCGIFFLAGS, \&req);
+</para>
+</foil>
+
</slides>
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