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Re: fstat st_size on open files on Parallels filesystem is wrong
- From: lennox at cs dot columbia dot edu
- To: cygwin at cygwin dot com
- Date: Mon, 21 Apr 2014 14:46:43 -0400
- Subject: Re: fstat st_size on open files on Parallels filesystem is wrong
- Authentication-results: sourceware.org; auth=none
- References: <21333 dot 25325 dot 11106 dot 958642 at compute01 dot cs dot columbia dot edu> <227151856 dot 20140421223417 at yandex dot ru>
On Monday, April 21 2014, "Andrey Repin" wrote to "lennox at
cs.columbia.edu, cygwin at cygwin.com" saying:
> Greetings, lennox at cs.columbia.edu!
> > Iâm running cygwin64 1.7.29 in a Windows 8.1 Pro virtual machine, running in
> > Parallels Desktop 9.0.24229 on Mac OS X 10.9.2.
> > Parallels Desktop automatically mounts my Mac OS X home directory as a Z:
> > drive in Windows. Cygwin mount reports this drive as being type "prlsf".
> > Unfortunately, I've discovered that if I have an open file on this
> > filesystem which has been written to, the size returned by Cygwin fstat() on
> > the open file is wrong. A stat() of the file after it's been closed is
> > correct.
> > This has the consequence that emacs always thinks saved files have been
> > modified externally, since emacs looks at files' sizes (as well as their
> > modification times) to detect external changes. This makes emacs
> > near-unusable.
> > This problem does not occur for files in my Cygwin home directory, or other
> > locations mounted on my Windows C: drive.
> > I've attached a simple unit test program that illustrates the problem.
> > I've also attached my cygcheck -s -v -r output.
> > Any ideas? Is this a Cygwin bug, a Parallels bug, or something else?
> > Glancing over the Cygwin code, I see that there are a few cases where fstat
> > has special cases for certain filesystem types.
> You never flushing the buffer in your test code, or I'm reading it wrong?
This is using Posix APIs -- open() / write() -- not C APIs, fopen() /
fwrite(), so there shouldn't be a buffer? Notice that the test behaves as I
expect for a file on NTFS.
Adding a call to fsync() prior to the fstat() call doesn't change anything.
I've modeled this as closely as I could on what it appears emacs is doing,
as far as I could tell.
lennox at cs.columbia.edu
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