El Wed, 08 Oct 2008 08:51:51 +0200, Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> escribió: > either dup() the fd or open() the file twice. There is absolutely no > valid reason to have two threads read from the same fd without > synchronising their access to it - never. In case this is the final consensus, I think that a topic that is brought to the list every few months and even generates (aparently not neccesary) patches is a hint that there should be somewhere a commentary (*) like this: (*) I don't know if what I wrote is 100% correct. Signed-off-by: Diego Calleja García <diegocg@xxxxxxxxx> Index: 2.6/include/linux/fs.h =================================================================== --- 2.6.orig/include/linux/fs.h 2008-10-09 00:06:50.000000000 +0200 +++ 2.6/include/linux/fs.h 2008-10-09 00:29:03.000000000 +0200 @@ -821,6 +821,18 @@ atomic_long_t f_count; unsigned int f_flags; mode_t f_mode; + /* + * Linux does NOT guarantee atomic reading/writing to file->f_pos in + * multithread apps running in 32 bit machines. There're several + * reasons for this behaviour: + * - Specifications don't say it must be implemented that way. + * - This behaviour is part of the Linux semantics. + * - Any application that does multithreaded access to file->f_pos + * should be doing its own locking: the processes should synchronize + * themselves when accessing a file descriptor. If an application + * doesn't do that, its file descriptor handling is buggy anyway and + * must be fixed to access file->f_pos properly. + */ loff_t f_pos; struct fown_struct f_owner; unsigned int f_uid, f_gid; -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
