Re: O_NONBLOCK, read(), select(), NFS, Ext2, etc.
Michael Rothwell ([EMAIL PROTECTED]) wrote: > How about using fcntl(), O_ASYNC and SIGIO? Don't think that's supported for disk files yet, at least by the kernel. glibc does aio emulation with threads, which isn't great. > Or maybe a broader question: > what's the preferred/working way to do async file i/o on Linux? SGI has done lots of work on this, using kernel threads; they don't have a patch yet for 2.4.0, but they do support 2.2.17 and 2.4.0-test10. TUX uses async I/O, I think, but it's inside the kernel. I hear plans are afoot for giving userspace async I/O that avoids creating threads; that should be more scalable than SGI's approach, if it ever happens. See http://www.kegel.com/c10k.html#aio for links and a few notes. - Dan - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] Please read the FAQ at http://www.tux.org/lkml/
Re: O_NONBLOCK, read(), select(), NFS, Ext2, etc.
On Fri, Jan 12, 2001 at 09:40:55AM +, Alan Cox wrote: > > be true; but perhaps I am doing something wrong. If I open() a file (on > > 2.2.18) from a floppy or NFS mount (to test in a slow environment) with > > O_NONBLOCK|O_RDONLY, read() will still block. If I try to select() on > > the file descriptor, select() always returns 0. > > The definition of immediate is not 'instant'. Otherwise no I/O system would > ever return anything but -EWOULDBLOCK. Its that it won't wait when there is > no data pending. On a floppy there is always data pending I have a long standing idea on modifying poll/read/write behavior on regular files opened in O_NONBLOCK mode. How about the following scheme: * poll returns POLLIN/POLLOUT on regular files only if the data are in buffer cache/there is room for write(). * read returns EAGAIN if the data are not in buffer cache. * write returns EAGAIN if there is no room (yet) to store the data. All the operation should signal to IO subsystem that the data are needed in cache/the room has to be freed. -- Alexander. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] Please read the FAQ at http://www.tux.org/lkml/
Re: O_NONBLOCK, read(), select(), NFS, Ext2, etc.
From: Chris Wedgwood <[EMAIL PROTECTED]> On Thu, Jan 11, 2001 at 09:34:08PM -0500, Michael Rothwell wrote: The man pages for open, read and write say that if a file is opened using the O_NONBLOCK flag, then read() and write() will always return immediately and not block the calling process. the man pages are wrong Don't you think cc'ing the man page maintainer [[EMAIL PROTECTED]] would be a good idea whenever you think something is wrong in the man pages? You never know, they might even improve. In this particular case I don't think anything is actually wrong, but I can well imagine that someone can invent clearer wording. It would also be useful to more clearly separate POSIX-mandated behaviour and actual Linux behaviour. Suggestions and patches are welcome as always. Andries - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] Please read the FAQ at http://www.tux.org/lkml/
Re: O_NONBLOCK, read(), select(), NFS, Ext2, etc.
Alan Cox wrote: > > > using the O_NONBLOCK flag, then read() and write() will always return > > immediately and not block the calling process. This does not appear to > > be true; but perhaps I am doing something wrong. If I open() a file (on > > 2.2.18) from a floppy or NFS mount (to test in a slow environment) with > > O_NONBLOCK|O_RDONLY, read() will still block. If I try to select() on > > the file descriptor, select() always returns 0. > > The definition of immediate is not 'instant'. Otherwise no I/O system would > ever return anything but -EWOULDBLOCK. Its that it won't wait when there is > no data pending. On a floppy there is always data pending How about using fcntl(), O_ASYNC and SIGIO? Or maybe a broader question: what's the preferred/working way to do async file i/o on Linux? -M - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] Please read the FAQ at http://www.tux.org/lkml/
Re: O_NONBLOCK, read(), select(), NFS, Ext2, etc.
> using the O_NONBLOCK flag, then read() and write() will always return > immediately and not block the calling process. This does not appear to > be true; but perhaps I am doing something wrong. If I open() a file (on > 2.2.18) from a floppy or NFS mount (to test in a slow environment) with > O_NONBLOCK|O_RDONLY, read() will still block. If I try to select() on > the file descriptor, select() always returns 0. The definition of immediate is not 'instant'. Otherwise no I/O system would ever return anything but -EWOULDBLOCK. Its that it won't wait when there is no data pending. On a floppy there is always data pending - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] Please read the FAQ at http://www.tux.org/lkml/
Re: O_NONBLOCK, read(), select(), NFS, Ext2, etc.
using the O_NONBLOCK flag, then read() and write() will always return immediately and not block the calling process. This does not appear to be true; but perhaps I am doing something wrong. If I open() a file (on 2.2.18) from a floppy or NFS mount (to test in a slow environment) with O_NONBLOCK|O_RDONLY, read() will still block. If I try to select() on the file descriptor, select() always returns 0. The definition of immediate is not 'instant'. Otherwise no I/O system would ever return anything but -EWOULDBLOCK. Its that it won't wait when there is no data pending. On a floppy there is always data pending - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] Please read the FAQ at http://www.tux.org/lkml/
Re: O_NONBLOCK, read(), select(), NFS, Ext2, etc.
Alan Cox wrote: using the O_NONBLOCK flag, then read() and write() will always return immediately and not block the calling process. This does not appear to be true; but perhaps I am doing something wrong. If I open() a file (on 2.2.18) from a floppy or NFS mount (to test in a slow environment) with O_NONBLOCK|O_RDONLY, read() will still block. If I try to select() on the file descriptor, select() always returns 0. The definition of immediate is not 'instant'. Otherwise no I/O system would ever return anything but -EWOULDBLOCK. Its that it won't wait when there is no data pending. On a floppy there is always data pending How about using fcntl(), O_ASYNC and SIGIO? Or maybe a broader question: what's the preferred/working way to do async file i/o on Linux? -M - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] Please read the FAQ at http://www.tux.org/lkml/
Re: O_NONBLOCK, read(), select(), NFS, Ext2, etc.
From: Chris Wedgwood [EMAIL PROTECTED] On Thu, Jan 11, 2001 at 09:34:08PM -0500, Michael Rothwell wrote: The man pages for open, read and write say that if a file is opened using the O_NONBLOCK flag, then read() and write() will always return immediately and not block the calling process. the man pages are wrong Don't you think cc'ing the man page maintainer [[EMAIL PROTECTED]] would be a good idea whenever you think something is wrong in the man pages? You never know, they might even improve. In this particular case I don't think anything is actually wrong, but I can well imagine that someone can invent clearer wording. It would also be useful to more clearly separate POSIX-mandated behaviour and actual Linux behaviour. Suggestions and patches are welcome as always. Andries - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] Please read the FAQ at http://www.tux.org/lkml/
Re: O_NONBLOCK, read(), select(), NFS, Ext2, etc.
On Fri, Jan 12, 2001 at 09:40:55AM +, Alan Cox wrote: be true; but perhaps I am doing something wrong. If I open() a file (on 2.2.18) from a floppy or NFS mount (to test in a slow environment) with O_NONBLOCK|O_RDONLY, read() will still block. If I try to select() on the file descriptor, select() always returns 0. The definition of immediate is not 'instant'. Otherwise no I/O system would ever return anything but -EWOULDBLOCK. Its that it won't wait when there is no data pending. On a floppy there is always data pending I have a long standing idea on modifying poll/read/write behavior on regular files opened in O_NONBLOCK mode. How about the following scheme: * poll returns POLLIN/POLLOUT on regular files only if the data are in buffer cache/there is room for write(). * read returns EAGAIN if the data are not in buffer cache. * write returns EAGAIN if there is no room (yet) to store the data. All the operation should signal to IO subsystem that the data are needed in cache/the room has to be freed. -- Alexander. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] Please read the FAQ at http://www.tux.org/lkml/
Re: O_NONBLOCK, read(), select(), NFS, Ext2, etc.
Michael Rothwell ([EMAIL PROTECTED]) wrote: How about using fcntl(), O_ASYNC and SIGIO? Don't think that's supported for disk files yet, at least by the kernel. glibc does aio emulation with threads, which isn't great. Or maybe a broader question: what's the preferred/working way to do async file i/o on Linux? SGI has done lots of work on this, using kernel threads; they don't have a patch yet for 2.4.0, but they do support 2.2.17 and 2.4.0-test10. TUX uses async I/O, I think, but it's inside the kernel. I hear plans are afoot for giving userspace async I/O that avoids creating threads; that should be more scalable than SGI's approach, if it ever happens. See http://www.kegel.com/c10k.html#aio for links and a few notes. - Dan - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] Please read the FAQ at http://www.tux.org/lkml/
O_NONBLOCK, read(), select(), NFS, Ext2, etc.
The man pages for open, read and write say that if a file is opened using the O_NONBLOCK flag, then read() and write() will always return immediately and not block the calling process. This does not appear to be true; but perhaps I am doing something wrong. If I open() a file (on 2.2.18) from a floppy or NFS mount (to test in a slow environment) with O_NONBLOCK|O_RDONLY, read() will still block. If I try to select() on the file descriptor, select() always returns 0. Is there a way to make open(), read() and write() live up to their manpages? -M - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] Please read the FAQ at http://www.tux.org/lkml/
O_NONBLOCK, read(), select(), NFS, Ext2, etc.
The man pages for open, read and write say that if a file is opened using the O_NONBLOCK flag, then read() and write() will always return immediately and not block the calling process. This does not appear to be true; but perhaps I am doing something wrong. If I open() a file (on 2.2.18) from a floppy or NFS mount (to test in a slow environment) with O_NONBLOCK|O_RDONLY, read() will still block. If I try to select() on the file descriptor, select() always returns 0. Is there a way to make open(), read() and write() live up to their manpages? -M - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] Please read the FAQ at http://www.tux.org/lkml/
