Intermec ck1 Reference Guide
Appendix A —
µClinux System
CK1 SDK Programmer’s Reference Manual
301
Accessing the devices and services that the files represent is done through
the system calls. The file system that you see is actually a user-level view of
the physical organization of the hard drive. When interacting with these
low-level components, the actual operation is done by the Kernel mode
through a system call. It provides methods for file-system calls like open,
close, and ioctl, which pass the control information to a device driver.
the system calls. The file system that you see is actually a user-level view of
the physical organization of the hard drive. When interacting with these
low-level components, the actual operation is done by the Kernel mode
through a system call. It provides methods for file-system calls like open,
close, and ioctl, which pass the control information to a device driver.
Linux also provides higher level interface services and devices. This action
is done through a standard library, which includes a set of functions that
can be used instead of the actual system calls. They are much more flexible
than the actual system calls, providing a buffered output. This way the
programmers do not have to take care of varying sizes of data blocks, and
the overhead of the system call is minimized.
is done through a standard library, which includes a set of functions that
can be used instead of the actual system calls. They are much more flexible
than the actual system calls, providing a buffered output. This way the
programmers do not have to take care of varying sizes of data blocks, and
the overhead of the system call is minimized.
One major advantage of Linux is that it supports a variety of different file
systems, which makes it exceedingly flexible and allows easy access to other
operating systems file systems. Nowadays, Linux supports a variety of
different file systems from different platforms, including msdos and vfat
from windows, Mac OS file system, and even the file system from Amiga.
Linux allows these file formats to be transparently mounted to the Linux
system through a common virtual file system (VFS). The VFS is actually a
kernel software layer providing all system calls related to a standard UNIX
file system. Supported file systems are invoked through this software layer
so that all file systems appear identical to the rest of the Linux kernel and
to the programs running in the Linux system. The function of VFS is
totally transparent to you, after you have mounted the accessed disk or
partition as part of the source tree file system to Linux. After the file
system operation is made, the kernel actually calls functions defined in
VFS-interface, which takes care of non-file system dependent operations
and forward the call to appropriate file system functions.
systems, which makes it exceedingly flexible and allows easy access to other
operating systems file systems. Nowadays, Linux supports a variety of
different file systems from different platforms, including msdos and vfat
from windows, Mac OS file system, and even the file system from Amiga.
Linux allows these file formats to be transparently mounted to the Linux
system through a common virtual file system (VFS). The VFS is actually a
kernel software layer providing all system calls related to a standard UNIX
file system. Supported file systems are invoked through this software layer
so that all file systems appear identical to the rest of the Linux kernel and
to the programs running in the Linux system. The function of VFS is
totally transparent to you, after you have mounted the accessed disk or
partition as part of the source tree file system to Linux. After the file
system operation is made, the kernel actually calls functions defined in
VFS-interface, which takes care of non-file system dependent operations
and forward the call to appropriate file system functions.
The VFS has to also take care of the modifications that you might do to
the files on a mounted file system. The write and read commands to the
different file systems are done through specified device drivers for the
different file systems. As the real file systems read data from the physical
disk, the block device driver is used to read physical blocks from the device
that they control. The files read from this block are then saved into a
buffer cache shared by all of the file systems and the Linux kernel. Here it
is buffered with an identifier according to its block number and a unique
identifier for the device that read it. This functionality enables the data
access to the same data without needing to retrieve it each time separately.
the files on a mounted file system. The write and read commands to the
different file systems are done through specified device drivers for the
different file systems. As the real file systems read data from the physical
disk, the block device driver is used to read physical blocks from the device
that they control. The files read from this block are then saved into a
buffer cache shared by all of the file systems and the Linux kernel. Here it
is buffered with an identifier according to its block number and a unique
identifier for the device that read it. This functionality enables the data
access to the same data without needing to retrieve it each time separately.
Networking Interface
Linux has a strong networking support, supporting many different
networking protocols including the most common TCP/UDP, IP, and
Ethernet. The networking messaging system is structured with several
different layers, each of the layers using the services of another, with
Internet protocol (IP) being at the heart of it. When an application
generates network traffic, it sends packets through the socket layers to a
transport layer (TCP or UDP), which forwards them to the IP layer. In
networking protocols including the most common TCP/UDP, IP, and
Ethernet. The networking messaging system is structured with several
different layers, each of the layers using the services of another, with
Internet protocol (IP) being at the heart of it. When an application
generates network traffic, it sends packets through the socket layers to a
transport layer (TCP or UDP), which forwards them to the IP layer. In