[PATCH] Change "strict sync" paramter from "no" to "yes" by default for 4.7.0.

Thu Mar 23 16:17:00 UTC 2017

On Thu, Mar 23, 2017 at 09:08:55AM -0700, Jeremy Allison via samba-technical wrote:
> On Thu, Mar 23, 2017 at 08:10:31AM -0700, Jeremy Allison via samba-technical wrote:
> > On Thu, Mar 23, 2017 at 03:34:22PM +0100, Christian Ambach via samba-technical wrote:
> > > > Thanks, I won't post a new version of the patch for
> > > > this but will fix if when I push if the consensus
> > > > is for accepting the change.
> > > 
> > > I consent to the change. Don't we need a patch for WHATSNEW as well?
> > 
> > Oh good point. Updated patch to follow.
> 
> Here it is with added WHATSNEW change.
> 
> Please review !
> 
> Jeremy.

Thank you.

Reviewed-by: Christof Schmitt <cs at samba.org>

> From 3192fa01c264c8a86633cbcff4250aec9c2075c4 Mon Sep 17 00:00:00 2001
> From: Jeremy Allison <jra at samba.org>
> Date: Wed, 22 Mar 2017 19:22:31 -0700
> Subject: [PATCH 1/2] s3: smbd: Change "strict sync" paramter from "no" to
>  "yes" for 4.7.0.
> 
> Document change and modify in loadparm.c.
> Safer default for new installs and vendors.
> 
> Signed-off-by: Jeremy Allison <jra at samba.org>
> ---
>  docs-xml/smbdotconf/tuning/strictsync.xml | 48 +++++++++++++++++++------------
>  source3/param/loadparm.c                  |  2 +-
>  2 files changed, 31 insertions(+), 19 deletions(-)
> 
> diff --git a/docs-xml/smbdotconf/tuning/strictsync.xml b/docs-xml/smbdotconf/tuning/strictsync.xml
> index 5cfd388..f2e3788 100644
> --- a/docs-xml/smbdotconf/tuning/strictsync.xml
> +++ b/docs-xml/smbdotconf/tuning/strictsync.xml
> @@ -3,26 +3,38 @@
>  				 type="boolean"
>                   xmlns:samba="http://www.samba.org/samba/DTD/samba-doc">
>   <description>
> -    <para>Many Windows applications (including the Windows 98 explorer
> -    shell) seem to confuse flushing buffer contents to disk with doing
> -    a sync to disk. Under UNIX, a sync call forces the thread to be
> -    suspended until the kernel has ensured that all outstanding data in
> -    kernel disk buffers has been safely stored onto stable storage.
> -    This is very slow and should only be done rarely. Setting this
> -    parameter to <constant>no</constant> (the default) means that
> -    <citerefentry><refentrytitle>smbd</refentrytitle>
> -    <manvolnum>8</manvolnum></citerefentry> ignores the Windows
> -    applications requests for a sync call. There is only a possibility
> -    of losing data if the operating system itself that Samba is running
> -    on crashes, so there is little danger in this default setting. In
> -    addition, this fixes many performance problems that people have
> -    reported with the new Windows98 explorer shell file copies.</para>
> +    <para>This parameter controls whether Samba honors a request
> +    from an SMB client to ensure any outstanding operating system
> +    buffer contents held in memory are safely written onto stable
> +    storage on disk. If set to <constant>yes</constant>, which is
> +    the default, then Windows applications can force the smbd server
> +    to synchronize unwritten data onto the disk. If set to
> +    <constant>no</constant> then smbd will ignore client
> +    requests to synchronize unwritten data onto stable storage on
> +    disk.</para>
> +
> +    <para>In Samba 4.7.0, the default for this parameter changed from
> +    <constant>no</constant> to <constant>yes</constant> to better
> +    match the expectations of SMB2/3 clients and improve application
> +    safety when running against smbd.</para>
> +
>      <para>The flush request from SMB2/3 clients is handled
> -    asynchronously, so for these clients setting the parameter
> -    to <constant>yes</constant> does not block the processing of other
> -    requests in the smbd process.</para>
> +    asynchronously inside smbd, so leaving the parameter as the default
> +    value of <constant>yes</constant> does not block the processing of
> +    other requests to the smbd process.</para>
> +
> +    <para>Legacy Windows applications (such as the Windows 98 explorer
> +    shell) seemed to confuse writing buffer contents to the operating
> +    system with synchronously writing outstanding data onto stable storage
> +    on disk. Changing this parameter to <constant>no</constant> means that
> +    <citerefentry><refentrytitle>smbd</refentrytitle>
> +    <manvolnum>8</manvolnum></citerefentry> will ignore the Windows
> +    applications request to synchronize unwritten data onto disk. Only
> +    consider changing this if smbd is serving obsolete SMB1 Windows clients
> +    prior to Windows XP (Windows 98 and below). There should be no need to
> +    change this setting for normal operations.</para>
>  </description>
>  
>  <related>sync always</related>
> -<value type="default">no</value>
> +<value type="default">yes</value>
>  </samba:parameter>
> diff --git a/source3/param/loadparm.c b/source3/param/loadparm.c
> index c65e613..57220a6 100644
> --- a/source3/param/loadparm.c
> +++ b/source3/param/loadparm.c
> @@ -207,7 +207,7 @@ static struct loadparm_service sDefault =
>  	.sync_always = false,
>  	.strict_allocate = false,
>  	.strict_rename = false,
> -	.strict_sync = false,
> +	.strict_sync = true,
>  	.mangling_char = '~',
>  	.copymap = NULL,
>  	.delete_readonly = false,
> -- 
> 2.7.4
> 
> 
> From 63a6313a87fca7df587a258110843eda04850d9b Mon Sep 17 00:00:00 2001
> From: Jeremy Allison <jra at samba.org>
> Date: Thu, 23 Mar 2017 09:06:27 -0700
> Subject: [PATCH 2/2] WHATSNEW: Document "strict sync" default change.
> 
> Signed-off-by: Jeremy Allison <jra at samba.org>
> ---
>  WHATSNEW.txt | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/WHATSNEW.txt b/WHATSNEW.txt
> index dd60cd2..cda61ef 100644
> --- a/WHATSNEW.txt
> +++ b/WHATSNEW.txt
> @@ -16,12 +16,18 @@ UPGRADING
>  NEW FEATURES/CHANGES
>  ====================
>  
> +The "strict sync" global parameter has been changed from
> +a default of "no" to "yes". This means smbd will by default
> +obey client requests to synchronize unwritten data in operating
> +system buffers safely onto disk. This is a safer default setting
> +for modern SMB1/2/3 clients.
>  
>  smb.conf changes
>  ================
>  
>    Parameter Name                Description             Default
>    --------------                -----------             -------
> +  strict sync			Default changed		yes
>  
>  
>  KNOWN ISSUES
> -- 
> 2.7.4
> 