Thanks Florin !! On 9/30/05, Florin Malita <fmalita@xxxxxxxxx> wrote: > On Fri, 30 Sep 2005 21:17:26 +0200 > Sebastian Skar <sebastianskar@xxxxxxxxx> wrote: > > we can see that the pointers are shallow copied (not 'copy constructed'...), > > so basically even across fork the same file position is relevant for > > both father and child. > > btw, this isn't linux specific - it's covered by POSIX and > documented in glibc: > > http://www.jaluna.com/doc/c5/html/ManPages/hman2posix/fork.2posix.html > > "The child process has its own copy of the parent's descriptors. These > descriptors reference the same underlying objects, so that, for > instance, file pointers in file objects are shared between the child > and the parent, so that an lseek(2POSIX) on a descriptor in the child > process can affect a subsequent read(2POSIX) or write(2POSIX) by the > parent." > > http://www.gnu.org/software/libc/manual/html_node/File-Position-Primitive.html > > "You can have multiple descriptors for the same file if you open the > file more than once, or if you duplicate a descriptor with dup. > Descriptors that come from separate calls to open have independent file > positions; using lseek on one descriptor has no effect on the other. > [...] > By contrast, descriptors made by duplication share a common file > position with the original descriptor that was duplicated. Anything > which alters the file position of one of the duplicates, including > reading or writing data, affects all of them alike." > > Cheers, > Florin > -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
