On Mar 18, 2017, at 5:47 PM, pedrom71 <[email protected]> wrote:
> I'm trying to write a new file with size > 64 gb using mono c# and Mono.Posix
> library, with the Syscall.pwrite() function. But in a 32-bit OS, I get error
> EOVERFLOW when the offset reach 4GB.
Because libMonoPosixHelper.so believes you can’t do that:
https://github.com/mono/mono/blob/9b824c3/support/unistd.c#L60-L67
Specifically, it asserts that your `offset` value can fit within a `off_t`. On
32-bit platforms, `off_t` is usually a 32-bit value, so your 64-bit value
cannot fit, so it returns EOVERFLOW.
Though I also see:
https://www.gnu.org/software/libc/manual/html_node/Feature-Test-Macros.html
> Macro: _FILE_OFFSET_BITS
> …
> If the macro is defined to the value 64, the large file interface replaces
> the old interface. I.e., the functions are not made available under different
> names (as they are with _LARGEFILE64_SOURCE).
This doesn’t mention what happens with `off_t`, but I also see:
http://users.suse.com/~aj/linux_lfs.html
> Compile your programs with "gcc -D_FILE_OFFSET_BITS=64". This forces all file
> access calls to use the 64 bit variants. Several types change also, e.g.
> off_t becomes off64_t.
This strongly implies that your libMonoPosixHelper.so isn’t being compiled with
`-D_FILE_OFFSET_BITS=64`. You should investigate the compilation flags that are
used when building within the mono/support directory.
- Jon
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