It is required to prevent deadlocks in single-threaded select-based IO
programs (namely: qrexec). POSIX API doesn't support checking how much
can be written to pipe/socket without blocking, so to prevent blocking
application must use O_NONBLOCK mode, and somehow deal with non-written
data (buffer it).
QubesOS/qubes-issues#1347
linux-utils/qrexec-lib/unpack.c:
Different compile errors will abort. Both different for fc20/21 but
based on same error below:
*
* FC21 ERROR: (but FC20 needs the code)
* unpack.c:31:0: error: "O_TMPFILE" redefined [-Werror]
* #define O_TMPFILE (__O_TMPFILE | O_DIRECTORY)
* ^
* In file included from /usr/include/bits/fcntl.h:61:0,
* from /usr/include/fcntl.h:35,
* from unpack.c:4:
* /usr/include/bits/fcntl-linux.h:151:0: note: this is the location of the previous definition
* # define O_TMPFILE __O_TMPFILE / * Atomically create nameless file. * /
* ^
* cc1: all warnings being treated as errors
* <builtin>: recipe for target 'unpack.o' failed
*/
/* #define O_TMPFILE (__O_TMPFILE | O_DIRECTORY) */
