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Subject[PATCH 06/17] drbd: fix confusing error message during attach
Date
If we attach a (consistent) backing device,
which knows about a last-agreed effective size,
and that effective size is *larger* than the currently requested size,
we refused to attach with ERR_DISK_TOO_SMALL
Failure: (111) Low.dev. smaller than requested DRBD-dev. size.
which is confusing to say the least.

This patch changes the error code in that case to ERR_IMPLICIT_SHRINK
Failure: (170) Implicit device shrinking not allowed. See kernel log.
additional info from kernel:
To-be-attached device has last effective > current size, and is consistent
(9999 > 7777 sectors). Refusing to attach.

It also allows to attach with an explicit size.

Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
---
drivers/block/drbd/drbd_nl.c | 49 ++++++++++++++++++++++++++++++++----
1 file changed, 44 insertions(+), 5 deletions(-)

diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index d02d38fd1288..e4774f720de5 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -127,6 +127,35 @@ static int drbd_msg_put_info(struct sk_buff *skb, const char *info)
return 0;
}

+__printf(2, 3)
+static int drbd_msg_sprintf_info(struct sk_buff *skb, const char *fmt, ...)
+{
+ va_list args;
+ struct nlattr *nla, *txt;
+ int err = -EMSGSIZE;
+ int len;
+
+ nla = nla_nest_start(skb, DRBD_NLA_CFG_REPLY);
+ if (!nla)
+ return err;
+
+ txt = nla_reserve(skb, T_info_text, 256);
+ if (!txt) {
+ nla_nest_cancel(skb, nla);
+ return err;
+ }
+ va_start(args, fmt);
+ len = vscnprintf(nla_data(txt), 256, fmt, args);
+ va_end(args);
+
+ /* maybe: retry with larger reserve, if truncated */
+ txt->nla_len = nla_attr_size(len+1);
+ nlmsg_trim(skb, (char*)txt + NLA_ALIGN(txt->nla_len));
+ nla_nest_end(skb, nla);
+
+ return 0;
+}
+
/* This would be a good candidate for a "pre_doit" hook,
* and per-family private info->pointers.
* But we need to stay compatible with older kernels.
@@ -1947,11 +1976,21 @@ int drbd_adm_attach(struct sk_buff *skb, struct genl_info *info)
}

/* Prevent shrinking of consistent devices ! */
- if (drbd_md_test_flag(nbc, MDF_CONSISTENT) &&
- drbd_new_dev_size(device, nbc, nbc->disk_conf->disk_size, 0) < nbc->md.la_size_sect) {
- drbd_warn(device, "refusing to truncate a consistent device\n");
- retcode = ERR_DISK_TOO_SMALL;
- goto force_diskless_dec;
+ {
+ unsigned long long nsz = drbd_new_dev_size(device, nbc, nbc->disk_conf->disk_size, 0);
+ unsigned long long eff = nbc->md.la_size_sect;
+ if (drbd_md_test_flag(nbc, MDF_CONSISTENT) && nsz < eff) {
+ if (nsz == nbc->disk_conf->disk_size) {
+ drbd_warn(device, "truncating a consistent device during attach (%llu < %llu)\n", nsz, eff);
+ } else {
+ drbd_warn(device, "refusing to truncate a consistent device (%llu < %llu)\n", nsz, eff);
+ drbd_msg_sprintf_info(adm_ctx.reply_skb,
+ "To-be-attached device has last effective > current size, and is consistent\n"
+ "(%llu > %llu sectors). Refusing to attach.", eff, nsz);
+ retcode = ERR_IMPLICIT_SHRINK;
+ goto force_diskless_dec;
+ }
+ }
}

lock_all_resources();
--
2.17.1
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