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<div class=Section1>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>It turns out that this bug was fixed last year<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText style='margin-left:.5in'><font size=1 face=Arial><span
style='font-size:9.0pt;font-family:Arial'>author Sebastian
Huber 2017-09-06
12:30:00 (UTC)<o:p></o:p></span></font></p>
<p class=MsoPlainText style='margin-left:.5in'><font size=1 face=Arial><span
style='font-size:9.0pt;font-family:Arial'>committer Sebastian
Huber 2017-09-06
12:40:38 (UTC)<o:p></o:p></span></font></p>
<p class=MsoPlainText style='margin-left:.5in'><font size=1 face=Arial><span
style='font-size:9.0pt;font-family:Arial'>dosfs: Fix fat_file_update()<o:p></o:p></span></font></p>
<p class=MsoPlainText style='margin-left:.5in'><font size=1 face=Arial><span
style='font-size:9.0pt;font-family:Arial'>Do not update the non-existant
meta-data of the root directory.<o:p></o:p></span></font></p>
<p class=MsoPlainText style='margin-left:.5in'><font size=1 face=Arial><span
style='font-size:9.0pt;font-family:Arial'>Close #2944.<o:p></o:p></span></font></p>
<p class=MsoPlainText style='margin-left:.5in'><font size=1 face=Arial><span
style='font-size:9.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>Apparently I have been working with an old snapshot of
dosfs. I hate it when that happens!<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>Sorry for not checking before posting a question.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>Cliff<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>-----Original Message-----<br>
From: Chris Johns<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>Sent: Tuesday, October 02, 2018 6:32 PM<br>
To: Cliff Geschke; <br>
Subject: Re: How to sync a dos file system externally</span></font><font
size=1 face=Arial><span style='font-size:9.0pt;font-family:Arial'><o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>On 03/10/2018 04:56, Cliff Geschke wrote:<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>> I have implemented a dos file system (msdos_*) on a
flash device.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>Is the flash device a chip you have direct access too? The
reason I ask is if<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>possible using JFFS2 (a journaling file system) or even
YAFFS (commercial<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>license maybe needed) is a better solution.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>> Because it is possible for the user to power down the
system unexpectedly, I<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>> want to sync the file system to the flash device after
a 3 second idle time. <o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>> How do I externally force a sync on msdos from another
thread?<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>The following test ...<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'> https://git.rtems.org/rtems/tree/testsuites/fstests/fsdosfssync01/init.c<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>shows how to purge a disk at the block layer. Wrap something
like this is the<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>way to purge the cache.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>> A related problem is that I use FTP (ftpd.c) to
externally read/write files on<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>> the msdos formatted flash. I have the idle
timeout set to 3 minutes for the FTP<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>> connection. After 3 minutes, ftpd issues a
chdir("/") which eventually calls<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>> msdos_free_node_info() that calls fat_file_close() and
may try to write out data<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>> to the flash. This is a problem because if the
power is turned off at that time<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>> the flash is corrupted.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>> <o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>> So whatever method I use to sync msdos needs to update
and write out the fat so<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>> that the subsequent msdos_free_node_info() does
nothing.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>I should point out there is a finite chance the disk can
still become corrupted.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>How small the window becomes depends on the system design,
for example how often<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>the disk is updated, power supply power down storage vs
media write time,<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>non-bricking read-only partitions, etc.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>I suspect triggering a timer to purge the cache as shown
above is no different<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>to lowering the `swapout` task's period. It has been a while
since I looked over<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>this code. The libblock cache implements separate threads to
"sync" the cache to<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>the media on a periodic basis. The cache's configuration
lets you set the<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>period. The values are documented here:<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>https://docs.rtems.org/doxygen/branches/master/group__rtems__bdbuf.html#define-members<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>This however raises a difficult question which is documented
in the code in a<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>comment:<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'> https://git.rtems.org/rtems/tree/cpukit/libblock/src/bdbuf.c#n1013<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>It is difficult when using a timer to know if the purge is
100% safe. If you can<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>arrange the purge call to happen after you know the update
has finished it<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>lowers the chance the disk maybe become corrupted.<o:p></o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoPlainText><font size=1 face=Arial><span style='font-size:9.0pt;
font-family:Arial'>Chris<o:p></o:p></span></font></p>
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