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[Eric Wheeler]

Good day all,

Today I was playing with lvmthin and did a metadata dump and restore with 
thin_dump.  I was low on space so I `thin_dump --repair`ed through gzip 
into restore.xml.gz, and hoped to

   zcat restore.xml.gz | thin_restore -i /proc/self/fd/0 -o /dev/mapper/pool-pool_tmeta

but it says /proc/self/fd/0 is "Not a regular file" ... which of course it isn't.

Watching lsof -o on thin_restore indicates a linear progression through 
the input (looks like a simple ifstream), so technically, I believe it 
could support this.


persistent-data/file_utils.cc:~57:
   persistent_data::check_file_exists(string const &file) does the 
"Regular file check."

It looks that persistent_data::check_file_exists is used in cache_restore 
and xml_parser::parse, both appear to read linearly without arbitrary seek 
so it might be safe to relax or modify that check.

Of course blindly skipping the "Not a regular file" bit might bypass 
possible problems if used to sanitize file existence elsewhere in the 
code---but at least for XML restores it would have saved me some time.

Please comment on whether or not this is a good idea and how it would best 
be implemented.  This is my first runthrough on the userspace thinp tools, 
so your input expertise is appreciated!

-Eric

--
Eric Wheeler
eWheeler Inc
www.ewheeler.net