NAME
Device::Blkid::E2fsprogs - Perl interface to e2fsprogs-based libblkid (v1.33 - v1.41.4)
SYNOPSIS
use Device::Blkid::E2fsprogs qw/ :funcs /;
# Get a cache object from libblkid, checking for exception
my $cache_file = '/etc/blkid/blkid.tab';
local $@;
my $cache - eval { get_cache($cache_file) };
if ($@) {
# Do something, log or die
die "Error while obtaining cache file: $@";
}
# Get the device associated with a given blkid LABEL
my $type = 'LABEL';
my $label = '/boot';
# Using the cache
my $devname = get_devname($type, $value, $cache);
# Get a Device::Blkid::E2fsprogs::Device object
my $device = get_dev($cache, $devname, $flags);
# Get device iterator, checking for exceptions
local $@;
my $dev_iter = eval { dev_iterate_begin($cache) };
if ($@) {
# Handle exception or not
}
# And now iterate over list of devices
if ( $device = dev_next($dev_iter) ) {
do_something_with_device($device);
}
# To explicitly force memory deallocation on an allocated object
undef $cache; Important Note
This library is only compatible with those versions of libblkid which shipped as a part of the e2fsprogs package, i.e., those versions of the library numbered 1.xx. While this package should work with the newer 2.xx.x versions of libblkid which are bundled with the util-linux-ng package, this is not recommended and will actually fail given the default library version checking which is done in the Makefile.PL configuration script. In most cases users would be advised to use Bastian Friedrich's util-linux-ng based Device::Blkid module as the newer lib interface is reportedly backward compatible with the old one anyway. Use of this package should be limited to those cases where the user is bound by constraint to the older, e2fsprogs versions of the library.
As all of the e2fsprogs versioned calls are present, if deprecated, in version 2.xx.x of the libblkid library, all older client code should be fully compatible with the new interface. There may, in practice, be problems with this assumption. As a result, if you are moving older, e2fsprogs compliant libblkid client code over to a system with version 2.xx.x of the library, you would be well advised to thoroughly test it for compatibility with the new interface.
Finally, this version has been implemented somewhat differently than Bastian's util-linux-ng build of the library. He opted to keep much of his logic and processing in XSUB, mine is done mostly in C; I have only used XSUB for my straight glue, everything else I have kept in C and have used the Perl API. This should not to be taken as any sort of statement about XS/XSUB but instead is simply a reflection of my own personal background and tastes.
DESCRIPTION
Libblkid provides a means of identifying block devices as to their content (such as filesystems) as well as allowing for the extraction of additional meta information such as filesystem labels, volume labels, serial numbers, device numbers, unique identifiers, etc. The libblkid library maintains a mapping of all of this composite information and maintains its association with a given block device on the system. UUID and label-based fstab(5) file configurations have become common in modern Linux distributions. Having the capability to abstract block devices in this way and to maintain mappings between volumes and storage devices can make managing multiple storage devices a much less daunting task.
This library provides for low level probing of block devices to access the various meta data associated with the particular partition or volume as well as access to an on disk cache file which contains mappings between this information and each block device on the system. Access to this cache file is one way in which unpriviledged users who do not have read access to the particular block device can gain access to this information. Users with the necessary access can always opt to probe the block device directly for this information.
This Perl extension to e2fsprogs-based versions of the libblkid library provides for the same access available from the C interface. It does not support the larger and more robust API which has been added and integrated into the libblkid library since its inclusion in the util-linux-ng package. That said, the libblkid which now ships with util-linux-ng is reportedly backward compatible with client code dependant upon the older, original library which would mean that this module should work with it, albeit with the more limited selection of API calls. Please see the preceding note for additional details regarding the differences between these two distinct versions of the library.
I have endeavored to provide a more Perlish interface to the library rather than just do straight mappings or wrappers over the C functions. Most library calls will return an undef on failure. Those which return data structures which are allocated in memory will throw an exception catchable via an eval/if. Furthermore, several of the original library calls which were passed in modifiable pointer arguments now return Perl hash representations of complex types where this made sense. See the interface documentation below for details on each call.
Please read the README file in the package archive for instructions should you encounter any problems while using this software package, as well as for instructions on building a debug version and how to report any problems which you might have.
It is worth noting that between versions 1.33 and 1.41.4, the entire period which libblkid was shipping as a part of the e2fsprogs package, the number of calls present in the API expanded from 17 in the original release of the library back in 2003 to 25 by the time it was migrated over to the util-linux-ng package in early 2009. This extension supports dynamic detection of the libblkid version on the target system from version 1.36 onward. In the event that a proper determination of version cannot be obtained and the library is confirmed to in fact be on the system, a default baseline version of 1.33 will be generated which will be compliant with all possible versions of libblkid which shipped with the e2fsprogs package.
INSTALLATION NOTES
This package has made use of a customized Devel::CheckLib module and Makefile.PL in an attempt to dynamically detect the version of libblkid currently installed on the target system and to then generate a PerlXS interface which directly targets and matches the interface of that libblkid version. This process is expected to work on all versions of libblkid later than v1.35. On versions 1.33 through to 1.35, a default baseline target for the v1.33 API is configured and built. Should you have any problems with this process, evident either in running the Makefile.PL or in running make against the resulting Makefile, please see the Makefile.PL for hints on troubleshooting. If you wish to report any problems with this version detection, please include any output from their installation process as well as a copy of your /usr/include/blkid/blkid.h file.
For additional details regarding dynamic library version detection, please refer to the README file at the top level of this package.
DEPENDENCIES
While this package is compatible with any version of e2fsprogs-based libblkid, dynamic version detection will only work on versions 1.36 and newer. In cases where the proper version cannot be detected, a baseline version of v1.33 will be generated.
EXPORT
Nothing is exported by default, but constants and package functions are available as follows:
To export libblkid defined constants, implement the following use pragma:
use Device::Blkid::E2fsprogs qw/ :consts /;To export this package's functions into the namespace, implement the following use pragma:
use Device::Blkid::E2fsprogs qw/ :funcs /;CONSTANTS
BLKID_DEV_CREATE-
Create and empty device structure if not found in the cache.
BLKID_DEV_VERIFY-
Make sure the device structure corresponds with reality.
BLKID_DEV_FIND-
Just look up a device entry and return undef if not found.
BLKID_DEV_NORMAL-
Get a valid device structure, either from the cache or by probing the block device.
FUNCTIONS
All function calls detailed below also contain the version of libblkid in which they first appeared as a part of the library. As has been noted above, all of these calls should also be valid in the newer util-linux-ng versions of this interface. Please note, when manually selecting a target version during initial package configuration and installation, make sure that you do not 'overshoot' the version which is actually installed otherwise installation of this package will fail. When in doubt, select dynamic version detection or accept the default baseline version, v1.33, which is a safe selection for any version of the library, keeping in mind of course that there may be "gaps" in the interface.
put_cache($cache)-
Write any changes to the blkid cache file and explicitly frees associated resources.
put_cache($cache)should be called after you have been doing any work with a cache object. Note, the cache object is freed by this call and as such must not be used by any subsequent operations. Further calls toput_cacheon an already deallocated cache structure result in a segfault from the libblkid library; it appears that this was never properly addressed, at least not in the e2fsprogs versions of this package.v1.33 get_cache($filename)-
Given a path to a cache file, return a blkid cache object reference. This reference is of type
Device::Blkid::E2fsprogs::Cache. As with other calls which allocate any object types, this call throws en exception on failure..v1.33 gc_cache($cache)-
Calling this performs a garbage cleanup on the specified cache by removing all non-existant devices.
v1.40 dev_devname($device)-
Given a blkid device object, returns a string representation of the device (e.g., /dev/sda3), or undef on fail. Device objects are of type
Device::Blkid::E2fsprogs::Device.v1.33 dev_iterate_begin($cache)-
Returns a device iterator object on the specified device cache. Device iterator objects are of type
Device::Blkid::E2fsprogs::DevIter. As in the case of other allocated types, this call throws an exception on fail.v1.33 dev_set_search($dev_iter, $type, $value)-
This function places a search filter on the specified device iterator based upon the criteria passed in on the final two arguments of the function. After this function has been called on the given iterator with a type and value argument, the iterator will only return onjects which match the specified criteria. Please note, the $type argument can also contain any valid blkid entity category, such as a LABEL or UUID tag for example.
# Set iterator to filter and match only on ext4 file systems dev_set_search($dev_iter, 'TYPE', 'ext4');A successful call returns a copy of the device iterator object being used, undef on fail.
v1.38 dev_next($dev_iter)-
Returns the next device object in the iteration. Check for undef as an end of list sentinal.
v1.33 dev_iterate_end($dev_iter)-
Frees the allocated iterator object from memory, although this is redundant; simply undef'ing the object to remove references to it or allowing it to go out of scope will also free the memory as well. Note, this call may be removed in a future version.
v1.33 devno_to_devname($devno)-
Given a device number, returns the associated device name (e.g., /dev/sda1) or undef if no match found.
v1.33 probe_all($cache)-
Given a valid cache object, probes the underlying block devices on the system. Returns the cache object instance on success, undef on fail.
v1.33 probe_all_new($cache)-
Given a valid cache object, probes for new block devices on the system. Returns the cache object instance on success, or undef in fail state.
v1.38 get_dev($cache, $devname, $flags)-
Returns a device object based upon the input criteria. Please refer to the constants sections to see what flags may be passed in to determine behaviour. Device objects are of type
Device::Blkid::E2fsprogs::Device. Throws exception on any failure to allocate the device object.v1.33 get_dev_size($devname)-
Given a device name, returns the size of the block device in bytes. Note, this underlying library call works with a file descriptor to the block device in question so you must have read access to the device being probed, usually as root or a member of the disk group, otherwise this call will fail and throw an exception. This call will also return undef should the actual libblkid call fail for any reason which does not generate an exception (i.e. a non-file descriptor related issue).
local $@; my $devsize = eval { get_dev_size('/dev/sda1') }; if ($@) { # Handle exception here, fd related problem }v1.33 known_fstype($fstype)-
Determines if a file system type is known to libblkid. If the file system is known, it returns the input file system argument string, otherwise undef.
v1.34 verify($cache, $device)-
Attempts to verify that the device object is a valid blkid device. Returns the instance of the current device object on success, otherwise undef is returned to indicate failure.
v1.36 get_tag_value($cache, $tagname, $devname)-
Given a valid $cache object, $tagname and $devname, this function returns the value to which the tag refers.
my $tagname = 'LABEL'; my $devname = '/dev/sda4'; my $tag_value = get_tag_value($cache, $tagname, $devname);v1.33 get_devname($cache, $token, $value)-
Similar to the last call, given a valid $cache object and $token and $value parameters, will return the device name of the specified block device (eg. /dev/sda1).
my $token = 'UUID'; my $value = '2b5c78cb-acc5-4ffa-83b6-deb099bb22cf'; my $devname = get_devname($cache, $token, $value);v1.33 tag_iterate_begin($device)-
Returns a tag iterater object on a valid device type, of type
Device::Blkid::E2fsprogs::TagIter. Any failure to allocate an iterator object results in a thrown exception.v1.33 tag_next($tag_iter)-
Returns a hash reference containing the next available tag pairing from the list, or undef is returned on failure.
{ type => "UUID", value => '83f076b3-7abd-4c32-83df-026e57373900' }v1.33 tag_iterate_end($tag_iter)-
Frees the memory allocated for the tag iterator object. This is redundant as the memory can be freed by removing references to the object, undef'ing it or allowing it to leave scope. Note, this call may be removed in a future version of this extension.
v1.33 dev_has_tag($device, $type, $value)-
Determines if the given device contains the specified tag. If it does, the device instance is returned, otherwise undef.
v1.38 find_dev_with_tag(cache, type, value)-
Given a tag type and value, crawls the blkid cache for a match and returns an instance of the device if found, undef on failure.
parse_tag_string()-
Given an tag pair input value in
type=valueformat, returns a hash reference to a hash containing the two constituent elements as key values. Returns undef in the event of a failure.{ type => 'LABEL', value => '/boot' }v1.33 parse_version_string($ver_string)-
Given a standard dotted-decimal style version string, returns a raw integer-like representation of the string, sans decimals.
v1.36 get_library_version()-
Returns a hash reference containing the libblkid library version and release date as well as a raw integer representation of the standard dotted-decimal formatted version string (see "parse_version_string" above). Returns undef on failure.
{ version => '1.41.4', date => '27-Jan-2009', raw => '1414' }v1.36
SEE ALSO
Device::Blkid - You should probably use this unless otherwise constrained.
This package project is also hosted on Github at git://github.com/raymroz/Device--Blkid--E2fsprogs.git
AUTHOR
Raymond Mroz, <mroz@cpan.org>
COPYRIGHT AND LICENSE
Copyright (C) 2010 by Raymond Mroz
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.10.1 or, at your option, any later version of Perl 5 you may have available.
TODO
Cleanup preprocessor code when everything checks out stable.
Consider eliminating redundant calls and implementing an even more 'Perlish' design.
Test scripts; handle multiple version targets.
CREDITS
I would like to thank Bastian Friedrich for his Device::Blkid. Given the scant supply of documentation available on libblkid, especially the older, e2fsprogs-based versions, his POD proved quite helpful as a source of documentation on the library and saved me a load of time. Thanks!
Thanks to David Cantrell, David Golden and Yasuhiro Matsumoto for Devel::CheckLib. I hacked it up a little bit to manage my dynamic version checks and build, hope you don't mind.
Thanks to Tom Erskine for your insight and experience in all things Perl.
I would also like to thank Larry McInnis for the loan of some hardware on which to develop this module. Most everything I have had been tied up and developing on the latest and greatest version of Debian didn't make much sense.
BUGS
What's a bug? :)
No known bugs at this time. That said, this module is largely written in C and does contain a number of memory allocations. While these allocations are done inside of libblkid itself, I do make every attempt to free the memory explicitly when I am done with it. That said, leaks are possible. Please report any issues as is detailed above.
DIRECTION
This is an early release of this module. It and its interface are subject to change at any time. Please refer to all package documentation before reporting any problems.
1 POD Error
The following errors were encountered while parsing the POD:
- Around line 529:
Unknown directive: =Cut