[PATCH v2 07/40] afs: Add comments on abort handling

David Howells
2023-12-13T13:50:22Z

Add some comments on AFS abort code handling in the rotation algorithm and
adjust the errors produced to match.

Reported-by: Jeffrey E Altman <jaltman@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeffrey Altman <jaltman@auristor.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
---
fs/afs/rotate.c | 101 ++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 90 insertions(+), 11 deletions(-)

diff --git a/fs/afs/rotate.c b/fs/afs/rotate.c
index a840c3588ebb..a3d127953ac6 100644
--- a/fs/afs/rotate.c
+++ b/fs/afs/rotate.c
@@ -13,6 +13,7 @@
#include <linux/sched/signal.h>
#include "internal.h"
#include "afs_fs.h"
+#include "protocol_uae.h"

/*
* Begin iteration through a server list, starting with the vnode's last used
@@ -143,6 +144,11 @@ bool afs_select_fileserver(struct afs_operation *op)
case -ECONNABORTED:
/* The far side rejected the operation on some grounds. This
* might involve the server being busy or the volume having been moved.
+ *
+ * Note that various V* errors should not be sent to a cache manager
+ * by a fileserver as they should be translated to more modern UAE*
+ * errors instead. IBM AFS and OpenAFS fileservers, however, do leak
+ * these abort codes.
*/
switch (op->ac.abort_code) {
case VNOVOL:
@@ -150,6 +156,11 @@ bool afs_select_fileserver(struct afs_operation *op)
* - May indicate that the VL is wrong - retry once and compare
* the results.
* - May indicate that the fileserver couldn't attach to the vol.
+ * - The volume might have been temporarily removed so that it can
+ * be replaced by a volume restore. "vos" might have ended one
+ * transaction and has yet to create the next.
+ * - The volume might not be blessed or might not be in-service
+ * (administrative action).
*/
if (op->flags & AFS_OPERATION_VNOVOL) {
op->error = -EREMOTEIO;
@@ -183,16 +194,56 @@ bool afs_select_fileserver(struct afs_operation *op)
_leave(" = t [vnovol]");
return true;

- case VSALVAGE: /* TODO: Should this return an error or iterate? */
case VVOLEXISTS:
- case VNOSERVICE:
case VONLINE:
- case VDISKFULL:
- case VOVERQUOTA:
- op->error = afs_abort_to_error(op->ac.abort_code);
+ /* These should not be returned from the fileserver. */
+ pr_warn("Fileserver returned unexpected abort %d\n",
+ op->ac.abort_code);
+ op->error = -EREMOTEIO;
+ goto next_server;
+
+ case VNOSERVICE:
+ /* Prior to AFS 3.2 VNOSERVICE was returned from the fileserver
+ * if the volume was neither in-service nor administratively
+ * blessed. All usage was replaced by VNOVOL because AFS 3.1 and
+ * earlier cache managers did not handle VNOSERVICE and assumed
+ * it was the client OSes errno 105.
+ *
+ * Starting with OpenAFS 1.4.8 VNOSERVICE was repurposed as the
+ * fileserver idle dead time error which was sent in place of
+ * RX_CALL_TIMEOUT (-3). The error was intended to be sent if the
+ * fileserver took too long to send a reply to the client.
+ * RX_CALL_TIMEOUT would have caused the cache manager to mark the
+ * server down whereas VNOSERVICE since AFS 3.2 would cause cache
+ * manager to temporarily (up to 15 minutes) mark the volume
+ * instance as unusable.
+ *
+ * The idle dead logic resulted in cache inconsistency since a
+ * state changing call that the cache manager assumed was dead
+ * could still be processed to completion by the fileserver. This
+ * logic was removed in OpenAFS 1.8.0 and VNOSERVICE is no longer
+ * returned. However, many 1.4.8 through 1.6.24 fileservers are
+ * still in existence.
+ *
+ * AuriStorFS fileservers have never returned VNOSERVICE.
+ *
+ * VNOSERVICE should be treated as an alias for RX_CALL_TIMEOUT.
+ */
+ case RX_CALL_TIMEOUT:
+ op->error = -ETIMEDOUT;
goto next_server;

+ case VSALVAGING: /* This error should not be leaked to cache managers
+ * but is from OpenAFS demand attach fileservers.
+ * It should be treated as an alias for VOFFLINE.
+ */
+ case VSALVAGE: /* VSALVAGE should be treated as a synonym of VOFFLINE */
case VOFFLINE:
+ /* The volume is in use by the volserver or another volume utility
+ * for an operation that might alter the contents. The volume is
+ * expected to come back but it might take a long time (could be
+ * days).
+ */
if (!test_and_set_bit(AFS_VOLUME_OFFLINE, &op->volume->flags)) {
afs_busy(op->volume, op->ac.abort_code);
clear_bit(AFS_VOLUME_BUSY, &op->volume->flags);
@@ -207,11 +258,20 @@ bool afs_select_fileserver(struct afs_operation *op)
}
goto busy;

- case VSALVAGING:
- case VRESTARTING:
+ case VRESTARTING: /* The fileserver is either shutting down or starting up. */
case VBUSY:
- /* Retry after going round all the servers unless we
- * have a file lock we need to maintain.
+ /* The volume is in use by the volserver or another volume
+ * utility for an operation that is not expected to alter the
+ * contents of the volume. VBUSY does not need to be returned
+ * for a ROVOL or BACKVOL bound to an ITBusy volserver
+ * transaction. The fileserver is permitted to continue serving
+ * content from ROVOLs and BACKVOLs during an ITBusy transaction
+ * because the content will not change. However, many fileserver
+ * releases do return VBUSY for ROVOL and BACKVOL instances under
+ * many circumstances.
+ *
+ * Retry after going round all the servers unless we have a file
+ * lock we need to maintain.
*/
if (op->flags & AFS_OPERATION_NO_VSLEEP) {
op->error = -EBUSY;
@@ -226,7 +286,7 @@ bool afs_select_fileserver(struct afs_operation *op)
if (!afs_sleep_and_retry(op))
goto failed;

- /* Retry with same server & address */
+ /* Retry with same server & address */
_leave(" = t [vbusy]");
return true;
}
@@ -270,10 +330,29 @@ bool afs_select_fileserver(struct afs_operation *op)

goto restart_from_beginning;

+ case VDISKFULL:
+ case UAENOSPC:
+ /* The partition is full. Only applies to RWVOLs.
+ * Translate locally and return ENOSPC.
+ * No replicas to failover to.
+ */
+ op->error = -ENOSPC;
+ goto failed_but_online;
+
+ case VOVERQUOTA:
+ case UAEDQUOT:
+ /* Volume is full. Only applies to RWVOLs.
+ * Translate locally and return EDQUOT.
+ * No replicas to failover to.
+ */
+ op->error = -EDQUOT;
+ goto failed_but_online;
+
default:
+ op->error = afs_abort_to_error(op->ac.abort_code);
+ failed_but_online:
clear_bit(AFS_VOLUME_OFFLINE, &op->volume->flags);
clear_bit(AFS_VOLUME_BUSY, &op->volume->flags);
- op->error = afs_abort_to_error(op->ac.abort_code);
goto failed;
}