pipe: add support for shrinking and growing pipes
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From: Michael Kerrisk on 20 Jun 2010 01:40 On Sat, Jun 19, 2010 at 8:13 PM, Jens Axboe <jaxboe(a)fusionio.com> wrote: > On 19/06/10 07.45, Michael Kerrisk wrote: >> Hello Jens, >> >> I've tested this F_SETPIPE_SZ code as it appears in 2.6.35-rc3, and >> things seem to work as advertised, if the text below is the correct >> advertisement. Could you please review the following man-pages text, >> and let me know if it's okay. >> >> fcntl.2: >> � � � �F_SETPIPE_SZ (long; since Linux 2.6.35) >> � � � � � � � Change �the �capacity of the pipe referred to by >> � � � � � � � fd to be at least arg �bytes. � An �unprivileged >> � � � � � � � process �can �adjust �the �pipe �capacity to any >> � � � � � � � value between the system page size and the limit >> � � � � � � � defined � in � /proc/sys/fs/pipe-size-max � (see >> � � � � � � � proc(5)). �Attempts to �set �the �pipe �capacity >> � � � � � � � below �the �page size are silently rounded up to >> � � � � � � � the page size. �Attempts by an unprivileged pro- >> � � � � � � � cess to set the pipe capacity above the limit in >> � � � � � � � /proc/sys/fs/pipe-size-max � yield � the � error >> � � � � � � � EPERM; �a �privileged process (CAP_SYS_RESOURCE) >> � � � � � � � can override the �limit. � When �allocating �the >> � � � � � � � buffer for the pipe, the kernel may use a capac- >> � � � � � � � ity larger than arg, if that is �convenient �for >> � � � � � � � the �implementation. �The F_GETPIPE_SZ operation >> � � � � � � � returns the actual size used. �Attempting to set >> � � � � � � � the �pipe �capacity �smaller �than the amount of >> � � � � � � � buffer space currently used to store �data �pro- >> � � � � � � � duces the error EBUSY. >> >> � � � �F_GETPIPE_SZ (void; since Linux 2.6.35) >> � � � � � � � Return �(as the function result) the capacity of >> � � � � � � � the pipe referred to by fd. >> >> And in proc.5: >> � � � �/proc/sys/fs/pipe-max-size (since Linux 2.6.35) >> � � � � � � � The value in this file defines �an �upper �limit >> � � � � � � � for �raising �the �capacity �of a pipe using the >> � � � � � � � fcntl(2) �F_SETPIPE_SZ �operation. � This �limit >> � � � � � � � applies �only �to �unprivileged �processes. �The >> � � � � � � � default value for this file is �1,048,576. � The >> � � � � � � � value �assigned �to �this �file �may �be rounded >> � � � � � � � upward, to reflect the value �actually �employed >> � � � � � � � for �a �convenient implementation. �To determine >> � � � � � � � the rounded-up value, display �the �contents �of >> � � � � � � � this �file �after �assigning a value to it. �The >> � � � � � � � minimum value that can be assigned to this �file >> � � � � � � � is the system page size. > > Looks good to me. Thanks! Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Author of "The Linux Programming Interface" http://blog.man7.org/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |