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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.
-
-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 /etc/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 (where the default is
-/etc/blkid.tab). 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);