From: KY Srinivasan <kys@microsoft.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC: "devel@linuxdriverproject.org" <devel@linuxdriverproject.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Dexuan Cui <decui@microsoft.com>
Subject: RE: [PATCH v2 1/2] Tools: hv: vssdaemon: report freeze errors
Thread-Topic: [PATCH v2 1/2] Tools: hv: vssdaemon: report freeze errors
Thread-Index: AQHP/QSXmC5vQj/BgE2XOkatyKGZIZxooquA
Date: Wed, 19 Nov 2014 23:12:57 +0000
Message-ID: <BN1PR0301MB0707937F69B155C862F028FFA0890@BN1PR0301MB0707.namprd03.prod.outlook.com>
References: <1415637422-27880-1-git-send-email-vkuznets@redhat.com>
 <1415637422-27880-2-git-send-email-vkuznets@redhat.com>
In-Reply-To: <1415637422-27880-2-git-send-email-vkuznets@redhat.com>
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> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@redhat.com]
> Sent: Monday, November 10, 2014 8:37 AM
> To: KY Srinivasan; Haiyang Zhang; Greg Kroah-Hartman
> Cc: devel@linuxdriverproject.org; linux-kernel@vger.kernel.org; Dexuan Cui
> Subject: [PATCH v2 1/2] Tools: hv: vssdaemon: report freeze errors
> 
> When ioctl(fd, FIFREEZE, 0) results in an error we cannot report it to syslog
> instantly since that can cause write to a frozen disk.
> However, the name of the filesystem which caused the error and errno are
> valuable and we would like to get a nice human-readable message in the log.
> Save errno before calling vss_operate(VSS_OP_THAW) and report the error
> right after.
> 
> Unfortunately, FITHAW errors cannot be reported the same way as we need
> to finish thawing all filesystems before calling syslog().
> 
> We should also avoid calling endmntent() for the second time in case we
> encountered an error during freezing of '/' as it usually results in SEGSEGV.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>

> ---
>  tools/hv/hv_vss_daemon.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/hv/hv_vss_daemon.c b/tools/hv/hv_vss_daemon.c index
> b720d8f..ee44f0d 100644
> --- a/tools/hv/hv_vss_daemon.c
> +++ b/tools/hv/hv_vss_daemon.c
> @@ -82,7 +82,7 @@ static int vss_operate(int operation)
>  	FILE *mounts;
>  	struct mntent *ent;
>  	unsigned int cmd;
> -	int error = 0, root_seen = 0;
> +	int error = 0, root_seen = 0, save_errno = 0;
> 
>  	switch (operation) {
>  	case VSS_OP_FREEZE:
> @@ -114,7 +114,6 @@ static int vss_operate(int operation)
>  		if (error && operation == VSS_OP_FREEZE)
>  			goto err;
>  	}
> -	endmntent(mounts);
> 
>  	if (root_seen) {
>  		error |= vss_do_freeze("/", cmd);
> @@ -122,10 +121,19 @@ static int vss_operate(int operation)
>  			goto err;
>  	}
> 
> -	return error;
> +	goto out;
>  err:
> -	endmntent(mounts);
> +	save_errno = errno;
>  	vss_operate(VSS_OP_THAW);
> +	/* Call syslog after we thaw all filesystems */
> +	if (ent)
> +		syslog(LOG_ERR, "FREEZE of %s failed; error:%d %s",
> +		       ent->mnt_dir, save_errno, strerror(save_errno));
> +	else
> +		syslog(LOG_ERR, "FREEZE of / failed; error:%d %s",
> save_errno,
> +		       strerror(save_errno));
> +out:
> +	endmntent(mounts);
>  	return error;
>  }
> 
> --
> 1.9.3

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