[AFS] prevent double cell registration

[Sven Schnelle <svens@stackframe.org>]

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kafs doesn't check if the cell already exists - so if you do an
echo "add newcell.org 1.2.3.4" >/proc/fs/afs/cells it will try to
create this cell again. kobject will also complain about a double
registration. To prevent such problems, return -EEXIST in that case.
---
 fs/afs/cell.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/fs/afs/cell.c b/fs/afs/cell.c
index 970d38f..87934b3 100644
--- a/fs/afs/cell.c
+++ b/fs/afs/cell.c
@@ -127,6 +127,15 @@ struct afs_cell *afs_cell_create(const char *name, char *vllist)
 
 	_enter("%s,%s", name, vllist);
 
+	read_lock(&afs_cells_lock);
+	list_for_each_entry(cell, &afs_cells, link) {
+		if(!strcasecmp(cell->name, name)) {
+			read_unlock(&afs_cells_lock);
+			return ERR_PTR(-EEXIST);
+		}
+	}
+	read_unlock(&afs_cells_lock);
+
 	cell = afs_cell_alloc(name, vllist);
 	if (IS_ERR(cell)) {
 		_leave(" = %ld", PTR_ERR(cell));
-- 
1.5.4.3


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