81 lines
3.2 KiB
Plaintext
81 lines
3.2 KiB
Plaintext
libblkid - a library to handle device identification and token extraction
|
|
|
|
Basic usage is as follows - there are two normal usage patterns:
|
|
|
|
For cases where a program wants information about multiple devices, or
|
|
expects to be doing multiple token searches, the program should
|
|
directly initialize cache file via (second parameter is cache
|
|
filename, NULL = default):
|
|
|
|
blkid_cache cache = NULL;
|
|
if (blkid_get_cache(&cache, NULL) < 0)
|
|
/* error reading the cache file, not really fatal */
|
|
|
|
Note that if no cache file exists, an empty cache struct is still
|
|
allocated. Usage of libblkid functions will use the cache to avoid
|
|
needless device scans.
|
|
|
|
The model of the blkid cache is that each device has a number of
|
|
attributes that can be associated with it. Currently the attributes
|
|
which are supported (and set) by blkid are:
|
|
|
|
TYPE filesystem type
|
|
UUID filesystem uuid
|
|
LABEL filesystem label
|
|
|
|
|
|
How to use libblkid? Normally, you either want to find a device with
|
|
a specific NAME=value token, or you want to output token(s) from a
|
|
device. To find a device that matches a following attribute, you
|
|
simply call the blkid_get_devname() function:
|
|
|
|
if ((devname = blkid_get_devname(cache, attribute_name, value))) {
|
|
/* do something with devname */
|
|
string_free(devname);
|
|
}
|
|
|
|
The cache parameter is optional; if it is NULL, then the blkid library
|
|
will load the default blkid.tab cache file, and then release the cache
|
|
before function call returns. The return value is an allocated string
|
|
which holds the resulting device name (if it is found). If the value
|
|
is NULL, then attribute_name is parsed as if it were
|
|
"<attribute_name>=<value>"; if it cannot be so parsed, then the
|
|
original attribute_name is returned in a copied allocated string.
|
|
This is a convenience to allow user programs to want to translate user
|
|
input, whether it is of the form: "/dev/hda1", "LABEL=root",
|
|
"UUID=082D-26E3", and get back a device name that it can use.
|
|
|
|
Alternatively, of course, the programmer can pass an attribute name of
|
|
"LABEL", and value of "root", if that is more convenient.
|
|
|
|
Another common usage is to retrieve the value of a specific attribute
|
|
for a particular device. This can be used to determine the filesystem
|
|
type, or label, or uuid for a particular device:
|
|
|
|
if ((value = blkid_get_tag_value(cache, attribute_name, devname))) {
|
|
/* do something with value */
|
|
string_free(value);
|
|
}
|
|
|
|
If a program needs to call multiple blkid functions, then passing in a
|
|
cache value of NULL is not recommended, since the blkid.tab file
|
|
will be repeatedly parsed over and over again, with memory allocated
|
|
and deallocated. To initialize the blkid cache, blkid_get_cache()
|
|
function is used:
|
|
|
|
if (blkid_get_cache(&cache, NULL) < 0)
|
|
goto errout;
|
|
|
|
The second parameter of blkid_get_cache (if non-zero) is the alternate filename
|
|
of the blkid cache file (see blkid man page for more information about the
|
|
default cache file location).
|
|
|
|
Normally, programs should just pass in NULL.
|
|
|
|
If you have called blkid_get_cache(), you should call blkid_put_cache()
|
|
when you are done using the blkid library functions. This will save the
|
|
cache to the blkid.tab file, if you have write access to the file. It
|
|
will also free all associated devices and tags:
|
|
|
|
blkid_put_cache(cache);
|