09-26-2016
What is the difference between o_direct and DAX with ext4 filesystem?
I'm trying to understand the difference between o_direct flag of open system call and dax (direct access) with ext4 filesystem.
According to my understanding both bypass page cache.
But I'm still unclear about the crucial difference between these 2 techniques. If there is a huge difference then what does it mean to use o_direct flag with DAX? Can anyone please explain about this in detail?
NOTE: Here I have partitioned a pmem device on top of DRAM using memmap parameter.
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LEARN ABOUT DEBIAN
pegasus-dax-validator
PEGASUS-DAX-VALIDA(1) PEGASUS-DAX-VALIDA(1)
NAME
pegasus-dax-validator - determines if a given DAX file is valid.
SYNOPSIS
pegasus-dax-validator daxfile [verbose]
DESCRIPTION
The pegasus-dax-validator is a simple application that determines, if a given DAX file is valid XML. For this, it parses the file with as
many XML validity checks that the Apache Xerces XML parser framework supports.
OPTIONS
daxfile
The location of the file containing the DAX.
verbose
If any kind of second argument was specified, not limited to the string verbose, the verbose output mode is switched on.
RETURN VALUE
If the DAX was parsed successfully, or only warning's were issued, the exit code is 0. Any 'error or fatal error will result in an exit
code of 1.
Additionally, a summary statistics with counts of warnings, errors, and fatal errors will be displayed.
EXAMPLE
The following shows the parsing of a DAX file that uses the wrong kind of value for certain enumerations. The output shows the errors with
the respective line number and column number of the input DAX file, so that one can find and fix them more easily. (The lines in the
example were broken to fit the manpage format.)
$ pegasus-dax-validator bd.dax
ERROR in line 14, col 110: cvc-enumeration-valid: Value 'i386' is not
facet-valid with respect to enumeration '[x86, x86_64, ppc, ppc_64,
ia64, sparcv7, sparcv9, amd64]'. It must be a value from the
enumeration.
ERROR in line 14, col 110: cvc-attribute.3: The value 'i386' of
attribute 'arch' on element 'executable' is not valid with respect to
its type, 'ArchitectureType'.
ERROR in line 14, col 110: cvc-enumeration-valid: Value 'darwin' is
not facet-valid with respect to enumeration '[aix, sunos, linux, macosx,
windows]'. It must be a value from the enumeration.
ERROR in line 14, col 110: cvc-attribute.3: The value 'darwin' of
attribute 'os' on element 'executable' is not valid with respect to
its type, 'OSType'.
0 warnings, 4 errors, and 0 fatal errors detected.
SEE ALSO
Apache Xerces-J http://xerces.apache.org/xerces2-j/
AUTHORS
Jens-S. Vockler <voeckler at isi dot edu>
Pegasus Team http://pegasus.isi.edu/
05/24/2012 PEGASUS-DAX-VALIDA(1)