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Copyright (C) 2009-2014, HGST, Inc.
Copyright (C) 2016, Western Digital.


I. Introduction

I.1. Overview

libzbc is a simple library providing functions for manipulating disks supporting the Zoned Block Command (ZBC) and Zoned-device ATA command set (ZAC) disks. libzbc implemention is compliant with the latest drafts of the ZBC and ZAC standards defined by INCITS technical committee T10 and T13 (respectively).

In addition to supporting ZBC and ZAC disks, libzbc also implements an emulation mode allowing emulating the behavior of a host-managed zoned disk using a regular file or a standard block device as backing store.

Several example applications using libzbc are available under the tools directory.

I.2. Library version

libzbc current major version is 5. Due to interface changes, this version is not compatible with previous libzbc versions (version 4.x). Overall, the library operation does not change, but applications written for previous libzbc versions must be updated to use the new API.

I.3. ZBC/ZAC Standards Versions Supported

The "master" code branch implements libzbc v5.0.0 which provide supports for the latest ZBC and ZAC standards (Rev 05).

Support for the older draft standards are available with previous releases and pre-releases (see https://github.com/hgst/libzbc/releases for details).

I.4. License

libzbc is distributed under the terms of the of the BSD 2-clause license ("Simplified BSD License" or "FreeBSD License"). A copy of this license with the library copyright can be found in the COPYING.BSD file.

All example applications under the tools directory are distributed under the terms of the GNU Lesser General Public License version 3, or any later version. A copy of version 3 of this license can be found in the COPYING.LESSER file.

libzbc and all its example applications are distributed "as is," without technical support, and WITHOUT ANY WARRANTY, without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. Along with libzbc, you should have received a copy of the BSD 2-clause license and of the GNU Lesser General Public License. If not, please see http://opensource.org/licenses/BSD-2-Clause and http://www.gnu.org/licenses/.

I.5. Contact and Bug Reports

To report problems, please contact:


II. Compilation and installation

II.1. Requiremensts

libzbc requires that the autoconf, automake and libtool development packages be installed on the host used for compilation.

The GTK3 and GTK3 development packages are necessary to compile of the gzbc application. Installing these packages will automatically enable the compilation of gzbc.

II.2. Compilation

To compile the library and all example applications under the tools directory, execute the following commands.

> sh ./autogen.sh
> ./configure
> make

II.3. Installation

To install the library and all example applications compiled under the tools directory, as root, execute the following command.

> make install

The library files are by default installed under /usr/lib (or /usr/lib64). The library header files are installed in /usr/include/libzbc. The executable files for the example applications are installed under /usr/bin. These defaults can be changed using the configure script.

Executing the following command displays the options used to control the installation pathes.

> ./configure --help

II.4. Compilation for device tests

The test directory contains several test programs and scripts allowing testing the compatibility of libzbc with a particular device. That is, testing if a device follows the same standard as currently supported by libzbc (see section I.2). The compilation of these test programs is disabled by default.

To compile the test programs, libzbc must be configured as follows.

> ./configure --with-test

The test programs and scripts are not affected by the execution of "make install". All defined tests must be executed directly form the test directory using the zbc_test.sh script. To test the device /dev/, the following can be executed.

> cd test
> sudo ./zbc_test.sh /dev/<SG node>

By default, all test cases will be executed. Detailed control of the test execution is possible using the options "-e" (execute) and "-s" (skip). Execute zbc_test.sh --help for details.

libzbc tests check the detailed error output from the device for invalid commands. This detailed error output cannot be obtained for a device being accessed using the block device backend driver. Specifying a block device file for the tests will thus result in many failed tests. For block device files, tests must be executed using the SG node of the block device. The SG node of a block device can be easily identified with the command "lsscsi -g". Note that for an emulated device, a block device file can be specified.

Each test executed outputs a log file in the test/log directory. These files can be consulted in case of failed test to identify the reason for the test failure.

III. Usage

III.1 Kernel Version

libzbc functions operate using device handles which are obtained by executing the zbc_open function. The path specified to identify a device can point to a regular file, a block device file or an SG node device file (/dev/sg).

As host-aware devices are background compatible with regular block device files (device type/signature 0x00), a host-aware device will always be accessible either through a block device file as well as its SG node device file.

For host-managed devices, the different device type/signature requires kernel support for block device files to be created. Kernel level support for host-managed block devices has been added to Linux kernel 4.10. For older kernels, host-managed devices will be accessible only through their SG node device files. Kernel support for the ZAC host-managed device signature (0xabcd) was introduced in kernel 3.19. Any kernel older than this version will not create an SG node device file for ZAC host-managed devices connected to a SATA port on the target host.

Regular files and block device files for regular devices can be used to operate libzbc in emulation mode. This will enable exposing the target file or block device as a host-managed zoned block device.

III.2 Library Functions

libzbc provides functions for discovering the zone configuration of a zoned device and for accessing the device. Accesses to the device may result in changes to the device zones condition, attributes or state (such as a sequential zone write pointer location). These changes are not internally tracked by libzbc. The functions provided to obtain the device zone information only provide a "snapshot" of the zone condition and state when executed. It is the responsability of an application to implement tracking of the device zone changes (such as increment to a sequential zone write pointer as writes to the zone are executed) if necessary.

All libzbc functions, since version 5.0.0, use 512B sector unit for reporting zone information and as the addressing unit for device accesses, independently of the actual device logical block size. This unification in the unit used by all API functions can simplify application development by hiding potential differences in logical block sizes between devices. However, application programmers must be careful to always implement accesses (read or write) to the device in multiple of the logical block size for reading and writing a zone. Furthermore, on host-managed devices, write operations to sequential zones must be aligned on a multiple of the device physical block size.

The main functions provided are as follows.

Function Description
zbc_open() Open a zoned device
zbc_close() Close a zoned device
zbc_get_device_info() Get device information
zbc_report_nr_zones() Get the number of zones
Get zone information
zbc_zone_operation() Execute a zone operation
zbc_open_zone() Explicitely open a zone
zbc_close_zone() Close an open zone
zbc_finish_zone() Finish a zone
zbc_reset_zone() Reset a zone write pointer
zbc_pread() Read data from a zone
zbc_pwrite() Write data to a zone
zbc_flush() Flush data to disk

The current implementation of these functions is NOT thread safe. In particular, concurrent write operations by multiple threads to the same zone may result in write errors without write ordering control by the application.

Additionally, the following functions are also provided to facilitate application development and tests.

Function Description
zbc_set_log_level() Set log level of the library functions
zbc_device_is_zoned() Test if a device is a zoned block device
zbc_print_device_info() Print to a file (stream) a device information
zbc_device_type_str() Get a string description of a device type
zbc_device_model_str() Get a string description of a device model
zbc_zone_type_str() Get a string description of a zone type
zbc_zone_condition_str() Get a string description of a zone condition
zbc_errno() Return sense key and sense code of the last command executed
zbc_sk_str() Get a string description of a sense key
zbc_asc_ascq_str() Get a string description of a sense code

III.3 Native Mode Operation

Linux kernel older than version 4.10 do not create a block device file for host-managed ZBC and ZAC devices. As a result, these devices can only be accessed through their associated SG node (/dev/sgx device file). For these older kernels, opening a ZBC or ZAC host managed disk with libzbc must thus be done using the device SG node. For kernel versions 4.10 and beyond compiled with zoned block device support, a block device file will be created for host-managed devices.

For host-aware devices, the device block device file or its SG node can both be used to open the device.

Once the device is open, accesses to the device are done transparantly using the device handle returned by libzbc zbc_open function. Operations such as report zones, reset zone write pointer, etc. only need the device handle.

III.4 Emulation Mode Operation

libzbc can emulate host-managed disks operation using a regular file or a legacy standard block device file (regular disk or loopback device). The use of the library in such case is identical to the native mode case, assuming that the emulated device is first configured by executing the zbc_set_zones tool. For an emulated zoned block device setup using a regular block device, the block device file of the backend device must always be used. Using the backend device SG node file will not work.

III.5 Documentation

More detailed information on libzbc functions and data types is available through the comments in the file include/libzbc/zbc.h. This file has comments formatted with the doxygen convention. HTML files documenting libzbc API can be generated using the doxygen project file documentation/libzbc.doxygen.

> cd documentation
> doxygen libzbc.doxygen

IV. Example Applications

Under the tools directory, several simple applications are available as examples. These appliations are as follows.

IV.1. gzbc (tools/gui)

gzbc provides a graphical user interface showing zone information of a zoned device. It also displays the write status (write pointer position) of zones graphically using color coding (red for written space and green for unwritten space). Some operations on zones can also be executed directly from the interface (reset zone write pointer, open zone, close zone, etc).

IV.2. zbc_report_zones (tools/report_zones/)

This application illustrates the use of the zone reporting functions (zbc_report_zones, zbc_report_nr_zones, zbc_list_zones). It obtains the zone information of a device and displays it in readable form on the standard output.

IV.3. zbc_open_zone (tools/open_zone/)

This application illustrates the use of the zbc_open_zone function allowing opening a zone.

IV.4. zbc_close_zone (tools/close_zone/)

This application illustrates the use of the zbc_close_zone function allowing closing a zone.

IV.5. zbc_finish_zone (tools/finish_zone/)

This application illustrates the use of the zbc_finish_zone function allowing finishing a zone.

IV.6. zbc_reset_zone (tools/reset_zone/)

This application illustrates the use of the zbc_reset_write_pointer function allowing resetting the write pointer of a zone to the start LBA of the zone.

IV.7. zbc_read_zone (tools/read_zone/)

This application reads data from a zone, up to the zone write pointer location and either send the read data to the standard output or copy the data to a regular file. It implementation uses the function zbc_pread.

IV.8. zbc_write_zone (tools/write_zone/)

This application illustrates the use of the zbc_pwrite function which write data to a zone at the zone write pointer location.

IV.9. zbc_set_zones (tools/set_zones/)

This application can be used to initialize the ZBC emulation mode for a regular file or a raw standard block device.

IV.10. zbc_set_write_ptr (tools/set_write_ptr/)

This application can be used to set the write pointer of a zone of an emulated ZBC device to any LBA value (within the range of the specified zone). It is intended for testing purposes only and is not valid for native ZBC devices.

IV.11. zbc_info (tools/info/)

This application tests if a device file points to a physical SMR device supporting either ZBC or ZAC. This excludes the emulation mode implemented by libzbc on top of regular files or regular block devices. If the device is identified as SMR, some information about the device are displayed (device type, capacity, sector size, etc).