mirror of https://github.com/vitalif/e2fsprogs
Update libblkid documentation.
Fix tst_resolve to use latest blkid API's.bitmap-optimize
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2003-03-01 Theodore Ts'o <tytso@mit.edu>
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* libblkid.txt (token): New file which gives basic
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documentation to the libblkid library.
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2002-11-09 Theodore Ts'o <tytso@mit.edu>
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* Release of E2fsprogs 1.32
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@ -0,0 +1,55 @@
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libblkid - a library to handle device identification and token extraction
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Basic usage is as follows - there are two normal usage patterns:
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For cases where a program wants information about multiple devices, or
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expects to be doing multiple token searches, the program should directly
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initialize cache file via (second parameter is cache filename, NULL = default):
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blkid_cache cache = NULL;
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if (blkid_get_cache(&cache, NULL) < 0)
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/* error reading the cache file, not really fatal */
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Note that if no cache file exists, an empty cache struct is still allocated.
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Usage of libblkid functions will use the cache to avoid needless device scans.
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For cases where a program only wants to find a single token, or display
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information about a specific device, it is often not necessary to manually
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load the cache. For functions which deal with a single device, they will
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probe the device directly if no cache is given. For "get" functions which
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do searching, they will read/free the cache internally.
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How to use libblkid? Normally, you either want to find a device with a
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specific NAME=value token, or you want to output token(s) from a device.
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To locate a specific token, you can call:
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if ((devname = blkid_get_devname(cache, token, value))) {
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/* do something with devname */
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string_free(devname);
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}
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where cache is optionally loaded, token is either a "NAME=value" string,
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or "NAME" and value gives the desired value to look for. The return
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value is an allocated string which holds the resulting device name (if
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found) or "NAME" if we do not have a proper value, or NULL if a specific
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token was not found. This allows you to pass token = "/dev/hda1" or
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token = "LABEL=root" and get a valid device name back if possible. The
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returned string must be freed with "free(devname)".
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The other common usage is to want the value of a specific tag on a device.
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if ((value = blkid_get_tag_value(cache, tagname, devname))) {
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/* do something with value */
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string_free(value);
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}
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If you have directly loaded the cache from the program, you need to clean
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up by saving the cache (assuming you have write access to the cache, this
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happens automatically if you didn't load it directly), and freeing it (this
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will also free all associated devices/tags):
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blkid_put_cache(cache);
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In all cases, any data returned by the searching functions from the cache
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is first verified from disk to ensure that it is still valid.
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@ -1,5 +1,10 @@
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2003-03-01 Theodore Ts'o <tytso@mit.edu>
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* resolve.c (main): Update debugging test program so that it
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compiles with the latest blkid API changes.
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* libblkid.3.in: Update manual page to reflect recent API changes.
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* resolve.c (blkid_get_tag_value): If the passed-in cache is NULL,
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then get and release a temporary cache as a convenience to
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the calling application.
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@ -30,11 +30,6 @@ and is verified to still be valid before being returned to the user
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The cache file also allows unprivileged users (normally anyone other
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than root, or those not in the "disk" group) to locate devices by label/id.
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.P
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Functions with "get" in their name will first search the cache (if given)
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for the specified data, and failing that will search visible block devices
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for this information. Functions with "find" in their name will only search
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the existing cache data for the specified device.
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.P
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In situations where one is getting information about a single known device,
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it does not impact performance whether the cache is used or not (unless you
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are not able to read the block device directly). If you are dealing with
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@ -51,14 +46,14 @@ in this situation.
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.SH AUTHOR
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.B libblkid
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was written by Andreas Dilger for the ext2 filesystem utilties, with input
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from Ted Ts'o.
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from Ted Ts'o. The library was subsequently heavily modified by Ted Ts'o.
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.SH FILES
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.TP
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.I /etc/blkid.tab
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Caches data extracted from each recognized block device.
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.SH AVAILABILITY
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.B libblkid
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is part of the e2fsprogs package since version 1.25 and is available from
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is part of the e2fsprogs package since version 1.33 and is available from
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http://e2fsprogs.sourceforge.net.
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.SH COPYING
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.B libblkid
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@ -84,8 +79,6 @@ http://www.gnu.org/licenses/licenses.html#LGPL
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.BR blkid_put_cache (3),
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.BR blkid_get_dev (3),
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.BR blkid_probe_all (3),
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.BR blkid_free_dev (3),
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.BR blkid_find_tag_dev (3),
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.BR blkid_get_tagname_devname (3),
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.BR blkid_get_token (3),
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.BR blkid_get_devname (3),
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.BR blkid_get_tag_value (3),
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.BR blkid.tab (7)
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@ -127,7 +127,7 @@ int main(int argc, char **argv)
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}
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if (argv[2]) {
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value = blkid_get_tagname_devname(cache, argv[1], argv[2]);
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value = blkid_get_tag_value(cache, argv[1], argv[2]);
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printf("%s has tag %s=%s\n", argv[2], argv[1],
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value ? value : "<missing>");
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} else {
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