lsblk: allow to --sort by hidden column

For example:

	lsblk -o NAME --sort SIZE

prints NAMEs, but sort by SIZEs.

Signed-off-by: Karel Zak <kzak@redhat.com>

Documentation/TODO

@@ -64,13 +64,6 @@ libmount (mount/umount)
 
    (all this already supported by libmount)
 
-libsmartcols
------------
-
- - (!) add SCOLS_FL_HIDDEN flag to make it possible to hide a column. Then we 
-   can use such column in lsblk(8) to only sort lines, but do not print the column.
-
-     lsblk -o NAME --sort SIZE
 
 partx
 -----

misc-utils/lsblk.c

@@ -214,6 +214,7 @@ struct lsblk {
 	unsigned int nodeps:1;		/* don't print slaves/holders */
 	unsigned int scsi:1;		/* print only device with HCTL (SCSI) */
 	unsigned int paths:1;		/* print devnames with "/dev" prefix */
+	unsigned int sort_hidden:1;	/* sort column not between output columns */
 };
 
 struct lsblk *lsblk;	/* global handler */
@@ -1849,8 +1850,11 @@ int main(int argc, char *argv[])
 	if (nexcludes == 0 && nincludes == 0)
 		excludes[nexcludes++] = 1;	/* default: ignore RAM disks */
 
-	if (lsblk->sort_id >= 0 && column_id_to_number(lsblk->sort_id) < 0)
-		errx(EXIT_FAILURE, _("the sort column has to be among the output columns"));
+	if (lsblk->sort_id >= 0 && column_id_to_number(lsblk->sort_id) < 0) {
+		/* the sort column is not between output columns -- add as hidden */
+		add_column(columns, ncolumns++, lsblk->sort_id);
+		lsblk->sort_hidden = 1;
+	}
 
 	mnt_init_debug(0);
 	scols_init_debug(0);
@@ -1876,6 +1880,8 @@ int main(int argc, char *argv[])
 
 		if (!(scols_flags & LSBLK_TREE) && id == COL_NAME)
 			fl &= ~SCOLS_FL_TREE;
+		if (lsblk->sort_hidden && lsblk->sort_id == id)
+			fl |= SCOLS_FL_HIDDEN;
 
 		cl = scols_table_new_column(lsblk->table, ci->name, ci->whint, fl);
 		if (!cl) {