MySQL bug #60788: InnoDB crashes with an assertion failure when receiving a signal on pwrite()

Reporting http://bugs.mysql.com/bug.php?id=60788 on Launchpad so we can track our work on it and the status of the MySQL bug locally:

Description:
According to POSIX write()/pwrite() return -1 with errno set to EINTR when those calls
are interrupted by a signal before they write any data, or return the number of bytes
written if a signal is received after successfully writing some data.

Neither of those cases are handled correctly by InnoDB. Here is an example of pwrite()
returning -1 with errno set to EINTR:

InnoDB: Error: Write to file ./test/test.ibd failed at offset 0 5308416.
InnoDB: 983040 bytes should have been written, only -1 were written.
InnoDB: Operating system error number 4.
InnoDB: Check that your OS and file system support files of this size.
InnoDB: Check also that the disk is not full or a disk quota exceeded.
InnoDB: Error number 4 means 'Interrupted system call'.
InnoDB: Some operating system error numbers are described at
InnoDB: http://dev.mysql.com/doc/refman/5.1/en/operating-system-error-codes.html
InnoDB: Assertion failure in thread 1140169024 in file os/os0file.c line 4205
InnoDB: Failing assertion: ret
InnoDB: We intentionally generate a memory trap.

MyISAM is not affected by this problem because mysys handles those cases correctly by
restarting the write.

I think all of the above applies to reads as well.

How to repeat:
Examine the os_file_pwrite()/os_file_pread() code. Compare with how EINTR is handled in
my_pwrite()/my_pread().