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/
