Fork#38225: Emulate _fseeki64()/_ftelli64() API on legacy platforms.
Open Date: 2018-04-21 14:26
Last Update: 2018-11-26 18:15
URL for this Ticket:
https://osdn.net//projects/mingw/ticket/38225
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Last Changes/Comment on this Ticket:
2018-11-26 18:15 Updated by: keith
Comment:
I have performed a review of Mumit Kahn's mingw-fseek.c implementation; I
observe several minor issues, and at least one critical issue. The critical
issue is:–
• The fseek() wrapper sets a flag, to indicate that it has been called; this
flag is then reset on the next call to the fwrite() wrapper. In neither
case is there any attempt to associate the flag with any particular stream,
never mind to ensure that the fwrite() is directed to the stream on which
the fseek() was performed. In consequence, it is entirely possible that the
flag could have been reset before the fwrite() which needs to act on it is
performed.
Besides this critical issue, other non-critical issues include:–
• Unnecessary use of (ugly) low level Windows APIs, leading to excessive
complexity of the implementation.
• Unnecessary repeated calls to the _get_osfhandle() API, within a single
fwrite() wrapper call; this surely has a negative impact on performance.
• Two fseek() wrapper functions, where one would suffice; (all fseek()-alike
calls could be redirected a to single wrapper, in which a 64-bit offset
argument is passed).
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Ticket Status:
Reporter: keith
Owner: (None)
Type: Feature Request
Status: Open
Priority: 5 - Medium
MileStone: (None)
Component: WSL
Severity: 5 - Medium
Resolution: None
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Ticket details:
Although 32-bit Windows has supported operations on files larger than 2GB,
since at least WinNT4 and Win98, (and possibly earlier), Microsoft did not
introduce the _fseeki64() and _ftelli64() APIs until MSVCR80.DLL, (and
subsequently retrofitted it to MSVCRT.DLL, from WinVista onwards); prior to
this, random access support in large files was provided through lower level
APIs such as _lseeki64(), or native Windows API functions.
As noted in this mailing list query, and this subsequent follow-up thread, it
is practicable to emulate the _fseeki64() and _ftelli64() APIs, such that they
become available on legacy versions of Windows, which pre-date the formal
introduction of these APIs by Microsoft; however, previous efforts to do so may
not have been entirely robust. Hopefully, the attached patch will do a better
job.
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