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s3: smbd: Change "strict sync" paramter from "no" to "yes" for 4.7.0.

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Document change and modify in loadparm.c.
Safer default for new installs and vendors.

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Christof Schmitt <cs@samba.org>
This commit is contained in:
Jeremy Allison 2017-03-22 19:22:31 -07:00
parent a74fef0b90
commit ed483d8e57
3 changed files with 33 additions and 19 deletions
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48
docs-xml/smbdotconf/tuning/strictsync.xml
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@ -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>

2
lib/param/loadparm.c
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@ -2832,6 +2832,8 @@ struct loadparm_context *loadparm_init(TALLOC_CTX *mem_ctx)
lpcfg_do_global_parameter(lp_ctx, "strict locking", "Auto");
lpcfg_do_global_parameter(lp_ctx, "strict sync", "yes");
lpcfg_do_global_parameter(lp_ctx, "map readonly", "yes");
lpcfg_do_global_parameter(lp_ctx, "allow trusted domains", "yes");

2
source3/param/loadparm.c
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@ -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,