Open System Services System Calls Reference Manual (G06.29+, H06.08+, J06.03+)

spt_readvz(2) OSS System Calls Reference Manual
— If the O_NONBLOCK flag is not set, the spt_readvz() function blocks until
either some data is written or the pipe is closed by all processes that had opened
the pipe for writing.
— If the O_NONBLOCK flag is set, the spt_readvz() function returns the value -1
and sets errno to [EAGAIN].
When attempting to read from a socket and no data is currently available:
• If the O_NONBLOCK flag is not set, the spt_readvz() function blocks until data
becomes available or an error occurs.
• If the O_NONBLOCK flag is set, the spt_readvz() function returns the value -1 and
sets errno to [EWOULDBLOCK].
When attempting to read from a character special file that supports nonblocking reads, such as a
terminal, and no data is currently available:
• If the O_NONBLOCK flag is not set, the spt_readvz() function blocks until data
becomes available or an error occurs.
• If the O_NONBLOCK flag is set, the spt_readvz() function returns the value -1 and
sets errno to [EAGAIN].
If it is interrupted by a signal before it reads any data, the spt_readvz() function returns the
value -1 with errno set to [EINTR]. If it is interrupted by a signal after it has successfully read
some data, the spt_readvz() function returns the number of bytes read.
When reading from a device special file, the return of EOF has no effect on subsequent calls to
the spt_readvz() function. When modem disconnect is detected, an EOF is returned. The errno
variable is not set to [EIO].
Upon successful completion, the spt_readvz() function marks the st_atime field of the file for
update.
The iov_count parameter specifies the number of entries (buffers) in the iovec structure pointed
to by the iov parameter. Each iovec entry specifies the base address and length of an area in
memory where data should be placed. The spt_readvz() function always fills a buffer com-
pletely before proceeding to the next.
The iovec structure is defined in the sys/uio.h header file and contains entries with these
members:
caddr_t iov_base;
int iov_len;
Use on Guardian Objects
After a call to the fork(), tdm_fork(),ortdm_spawn() function, the initial position within a
Guardian EDIT file (a file in /G with file code 101) is the same for both parent and child
processes. However, the position is not shared; moving the current position from within one pro-
cess does not move it in the other process.
NOTES
For file descriptors for non-regular files, the spt_readvz() function behaves exactly the same as
spt_readvx(). For file descriptors for regular files, this is a thread-aware function: if this func-
tion must wait for an I/O operation to complete on an open file, this function blocks the thread
that called it (instead of the entire process), while it waits for the I/O operation to complete.
This function serializes file operations on an open file. If a thread calls spt_readvz() to access a
file that already has a file operation in progress by a different thread, this thread is blocked until
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