Is O_LARGEFILE needed just to write a large file?

c large-files file-descriptor posix-api large-file-support
Daniel Trebbien picture Daniel Trebbien · May 22, 2010 · Viewed 11k times · Source

Is the O_LARGEFILE flag needed if all that I want to do is write a large file (O_WRONLY) or append to a large file (O_APPEND | O_WRONLY)?

From a thread that I read titled "Cannot write >2gb index file" on the CLucene-dev mailing list, it appears that O_LARGEFILE might be needed to write large files, but participants in that discussion are using O_RDWR, not O_WRONLY, so I am not sure.

Answer

R.. GitHub STOP HELPING ICE picture R.. GitHub STOP HELPING ICE · Aug 6, 2010

O_LARGEFILE should never be used directly by applications. It's to be used internally by the 64-bit-offset-compatible version of open in libc when it makes the syscall to the kernel (Linux, or possibly another kernel with this 64-bit-offset-mode-is-a-second-class-citizen nonsense). Just make sure to always include -D_FILE_OFFSET_BITS=64 in your CFLAGS and you'll never have to worry about anything.

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