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Subject[PATCH] ipc/util.c: Cleanup and improve sysvipc_find_ipc(), V3
Date
sysvipc_find_ipc() can be simplified further:

- It uses a for() loop to locate the next entry in the idr.
This can be replaced with idr_get_next().

- It receives two parameters (pos - which is actually
an idr index and not a position, and new_pos, which
is really a position).
One parameter is sufficient.

Link: https://lore.kernel.org/all/20210903052020.3265-3-manfred@colorfullife.com/
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
---

Resending the patch, it seems it was stuck:
- typo noticed by Waiman corrected.
- rediffed
- retested

@Andrew: Could you add it it linux-next/mm?
It is in my outbox for > 6 months now, and using a for() loop instead of
idr_get_next() is just wrong.
And the variable naming should be cleaned up as well
(idx -> index, without sequence number. id -> user space id, with
sequence number. The current function doesn't follow that)

ipc/util.c | 53 ++++++++++++++++++++++++++++++++---------------------
1 file changed, 32 insertions(+), 21 deletions(-)

diff --git a/ipc/util.c b/ipc/util.c
index a2208d0f26b2..05cb9de66735 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -782,28 +782,37 @@ struct pid_namespace *ipc_seq_pid_ns(struct seq_file *s)
return iter->pid_ns;
}

-/*
- * This routine locks the ipc structure found at least at position pos.
+/**
+ * sysvipc_find_ipc - Find and lock the ipc structure based on seq pos
+ * @ids: ipc identifier set
+ * @pos: expected position
+ *
+ * The function finds an ipc structure, based on the sequence file
+ * position @pos. If there is no ipc structure at position @pos, then
+ * the successor is selected.
+ * If a structure is found, then it is locked (both rcu_read_lock() and
+ * ipc_lock_object()) and @pos is set to the position needed to locate
+ * the found ipc structure.
+ * If nothing is found (i.e. EOF), @pos is not modified.
+ *
+ * The function returns the found ipc structure, or NULL at EOF.
*/
-static struct kern_ipc_perm *sysvipc_find_ipc(struct ipc_ids *ids, loff_t pos,
- loff_t *new_pos)
+static struct kern_ipc_perm *sysvipc_find_ipc(struct ipc_ids *ids, loff_t *pos)
{
- struct kern_ipc_perm *ipc = NULL;
- int max_idx = ipc_get_maxidx(ids);
+ int tmpidx;
+ struct kern_ipc_perm *ipc;

- if (max_idx == -1 || pos > max_idx)
- goto out;
+ /* convert from position to idr index -> "-1" */
+ tmpidx = *pos - 1;

- for (; pos <= max_idx; pos++) {
- ipc = idr_find(&ids->ipcs_idr, pos);
- if (ipc != NULL) {
- rcu_read_lock();
- ipc_lock_object(ipc);
- break;
- }
+ ipc = idr_get_next(&ids->ipcs_idr, &tmpidx);
+ if (ipc != NULL) {
+ rcu_read_lock();
+ ipc_lock_object(ipc);
+
+ /* convert from idr index to position -> "+1" */
+ *pos = tmpidx + 1;
}
-out:
- *new_pos = pos + 1;
return ipc;
}

@@ -817,11 +826,13 @@ static void *sysvipc_proc_next(struct seq_file *s, void *it, loff_t *pos)
if (ipc && ipc != SEQ_START_TOKEN)
ipc_unlock(ipc);

- return sysvipc_find_ipc(&iter->ns->ids[iface->ids], *pos, pos);
+ /* Next -> search for *pos+1 */
+ (*pos)++;
+ return sysvipc_find_ipc(&iter->ns->ids[iface->ids], pos);
}

/*
- * File positions: pos 0 -> header, pos n -> ipc id = n - 1.
+ * File positions: pos 0 -> header, pos n -> ipc idx = n - 1.
* SeqFile iterator: iterator value locked ipc pointer or SEQ_TOKEN_START.
*/
static void *sysvipc_proc_start(struct seq_file *s, loff_t *pos)
@@ -846,8 +857,8 @@ static void *sysvipc_proc_start(struct seq_file *s, loff_t *pos)
if (*pos == 0)
return SEQ_START_TOKEN;

- /* Find the (pos-1)th ipc */
- return sysvipc_find_ipc(ids, *pos - 1, pos);
+ /* Otherwise return the correct ipc structure */
+ return sysvipc_find_ipc(ids, pos);
}

static void sysvipc_proc_stop(struct seq_file *s, void *it)
--
2.37.1
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