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Full Discussion: Lseek implementation
Top Forums UNIX for Dummies Questions & Answers Lseek implementation Post 302554793 by Humudituu on Tuesday 13th of September 2011 05:37:37 AM
Old 09-13-2011
Question Lseek implementation
Hi everybody,

i've been googling for ages now and gotten kinda desperate... The question, however, might be rather trivial for the experts: What is it exactly, i.e. physically, the POSIX function (for a file) "lseek" does? Does it trigger some kind of synchronization on disk? Is it just for the file system?

Rationale:
I'm am running some benchmarks to get an idea, how our system (ext4@Debian5) works. I'm having 100 threads reading or writing randomly small requests on disk (POSIX read/write with DIRECT_IO) -> read,lseek,read,lseek,... or write,lseek,write,lseek,... . The mean lseek response time while reading is marginally small, however, the mean lseek response time while writing is appr. as high as the mean response time of a write itself (several ms), and I don't know why...

Any help is appreciated.
 

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LEARN ABOUT FREEBSD

mac_free

MAC_FREE(3)						   BSD Library Functions Manual 					       MAC_FREE(3)

NAME

     mac_free -- free MAC label

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/mac.h>

     int
     mac_free(mac_t label);

DESCRIPTION

     The mac_free() function frees the storage allocated to contain a mac_t.

RETURN VALUES

     The mac_free() function always returns 0.	WARNING: see the notes in the BUGS section regarding the use of this function.

SEE ALSO

     mac(3), mac_get(3), mac_prepare(3), mac_set(3), mac_text(3), posix1e(3), mac(4), mac(9)

STANDARDS

     POSIX.1e is described in IEEE POSIX.1e draft 17.  Discussion of the draft continues on the cross-platform POSIX.1e implementation mailing
     list.  To join this list, see the FreeBSD POSIX.1e implementation page for more information.

HISTORY

     Support for Mandatory Access Control was introduced in FreeBSD 5.0 as part of the TrustedBSD Project.

BUGS

     POSIX.1e specifies that mac_free() will be used to free text strings created using mac_to_text(3).  Because mac_t is a complex structure in
     the TrustedBSD implementation, mac_free() is specific to mac_3, and must not be used to free the character strings returned from
     mac_to_text().  Doing so may result in undefined behavior.

BSD
								 December 21, 2001							       BSD
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