[PATCH] Do not break buffers in fvwrite for unbuffered files

[Federico Terraneo]

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While hunting a performance bottleneck related to writing files on a
microcontroller I noticed an inconsistency in newlib for unbuffered files.

While doing an fread() with a large buffer results in a call to read()
with the same buffer and size, a call to fwrite() breaks the buffer in
multiple calls to write() each up to BUFSIZ in size.

This may cause performance issues, and for reference glibc seems to even
try to pass large buffers untouched also if the files are fully
buffered, at least that's what a simple test using strace on Linux has
shown.

This simple patch makes the behaviour of fwrite() consistent with fread().


2013-10-21  Terraneo Federico  <fede.tft@hotmail.it>

	* libc/stdio/fvwrite.c: Do not break buffers for unbuffered
          files



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