From: Darrick J. Wong <djwong@kernel.org>
Date: Wed, 22 Jun 2022 19:28:52 +0000 (-0500)
Subject: xfs: create shadow transaction reservations for computing minimum log size
X-Git-Tag: v5.19.0-rc0~70
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=ad769a07b1cc00c1460abbb93d3f7aa14aa09912;p=thirdparty%2Fxfsprogs-dev.git

xfs: create shadow transaction reservations for computing minimum log size

Source kernel commit: 52d8ea4f2406c14d632a0e7f816bbb18d8c3e9ed

Every time someone changes the transaction reservation sizes, they
introduce potential compatibility problems if the changes affect the
minimum log size that we validate at mount time.  If the minimum log
size gets larger (which should be avoided because doing so presents a
serious risk of log livelock), filesystems created with old mkfs will
not mount on a newer kernel; if the minimum size shrinks, filesystems
created with newer mkfs will not mount on older kernels.

Therefore, enable the creation of a shadow log reservation structure
where we can "undo" the effects of tweaks when computing minimum log
sizes.  These shadow reservations should never be used in practice, but
they insulate us from perturbations in minimum log size.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
---

diff --git a/include/xfs_trace.h b/include/xfs_trace.h
index 79743f045..951ded3d5 100644
--- a/include/xfs_trace.h
+++ b/include/xfs_trace.h
@@ -194,6 +194,7 @@
 #define trace_xfs_trans_read_buf_recur(a)	((void) 0)
 #define trace_xfs_trans_read_buf(a)		((void) 0)
 #define trace_xfs_trans_commit(a,b)		((void) 0)
+#define trace_xfs_trans_resv_calc_minlogsize(a,b,c) ((void) 0)
 
 #define trace_xfs_defer_cancel(a,b)		((void) 0)
 #define trace_xfs_defer_pending_commit(a,b)	((void) 0)
diff --git a/libxfs/xfs_log_rlimit.c b/libxfs/xfs_log_rlimit.c
index 116178fdd..44300abcd 100644
--- a/libxfs/xfs_log_rlimit.c
+++ b/libxfs/xfs_log_rlimit.c
@@ -14,6 +14,7 @@
 #include "xfs_trans_space.h"
 #include "xfs_da_btree.h"
 #include "xfs_bmap_btree.h"
+#include "xfs_trace.h"
 
 /*
  * Calculate the maximum length in bytes that would be required for a local
@@ -46,19 +47,25 @@ xfs_log_get_max_trans_res(
 	struct xfs_mount	*mp,
 	struct xfs_trans_res	*max_resp)
 {
+	struct xfs_trans_resv	resv;
 	struct xfs_trans_res	*resp;
 	struct xfs_trans_res	*end_resp;
+	unsigned int		i;
 	int			log_space = 0;
 	int			attr_space;
 
 	attr_space = xfs_log_calc_max_attrsetm_res(mp);
 
-	resp = (struct xfs_trans_res *)M_RES(mp);
-	end_resp = (struct xfs_trans_res *)(M_RES(mp) + 1);
-	for (; resp < end_resp; resp++) {
+	memcpy(&resv, M_RES(mp), sizeof(struct xfs_trans_resv));
+
+	resp = (struct xfs_trans_res *)&resv;
+	end_resp = (struct xfs_trans_res *)(&resv + 1);
+	for (i = 0; resp < end_resp; i++, resp++) {
 		int		tmp = resp->tr_logcount > 1 ?
 				      resp->tr_logres * resp->tr_logcount :
 				      resp->tr_logres;
+
+		trace_xfs_trans_resv_calc_minlogsize(mp, i, resp);
 		if (log_space < tmp) {
 			log_space = tmp;
 			*max_resp = *resp;		/* struct copy */
@@ -66,7 +73,7 @@ xfs_log_get_max_trans_res(
 	}
 
 	if (attr_space > log_space) {
-		*max_resp = M_RES(mp)->tr_attrsetm;	/* struct copy */
+		*max_resp = resv.tr_attrsetm;	/* struct copy */
 		max_resp->tr_logres = attr_space;
 	}
 }