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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.
For cases where a program only wants to find a single token, or display
information about a specific device, it is often not necessary to manually
load the cache. For functions which deal with a single device, they will
probe the device directly if no cache is given. For "get" functions which
do searching, they will read/free the cache internally.
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 locate a specific token, you can call:
if ((devname = blkid_get_devname(cache, token, value))) {
/* do something with devname */
string_free(devname);
}
where cache is optionally loaded, token is either a "NAME=value" string,
or "NAME" and value gives the desired value to look for. The return
value is an allocated string which holds the resulting device name (if
found) or "NAME" if we do not have a proper value, or NULL if a specific
token was not found. This allows you to pass token = "/dev/hda1" or
token = "LABEL=root" and get a valid device name back if possible. The
returned string must be freed with "free(devname)".
The other common usage is to want the value of a specific tag on a device.
if ((value = blkid_get_tag_value(cache, tagname, devname))) {
/* do something with value */
string_free(value);
}
If you have directly loaded the cache from the program, you need to clean
up by saving the cache (assuming you have write access to the cache, this
happens automatically if you didn't load it directly), and freeing it (this
will also free all associated devices/tags):
blkid_put_cache(cache);
In all cases, any data returned by the searching functions from the cache
is first verified from disk to ensure that it is still valid.
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