Hi, Pradeep Singh wrote: > there is a field like sync_fs( struct super_block *sb, int wait ) and void > write_inode( struct inode *inode, int wait ) . > > i got wat it meant but the wait parameter is used to specify whether the > operation should b synchronous or not. Right. > how does it ensures synchronisation and with whom ?? ? If "wait" is TRUE, then the function will not return until the synchronisation (of the filesystem in the case of sync_fs and of the inode in the case of write_inode) has been done. On the contrary, if you call these functions with "wait" equal to FALSE, then it means that you request a synchronisation, but the function will return before the data will be really written to the disk. Have a look at http://lxr.linux.no/source/fs/ext2/inode.c#L1224, which is in the implementation of the ext2 write inode: 1224 mark_buffer_dirty(bh); 1225 if (do_sync) { 1226 sync_dirty_buffer(bh); 1227 if (buffer_req(bh) && !buffer_uptodate(bh)) { 1228 printk ("IO error syncing ext2 inode [%s:%08lx]\n", 1229 sb->s_id, (unsigned long) ino); 1230 err = -EIO; 1231 } 1232 } (do_sync is the "wait" parameter we discussed above). If you look at the code of sync_dirty_buffer(), it's in fact doing a wait_on_buffer(), which will wait for the completion of the operation. > my ques is when and how does sys_read() and sys_write() pass control to the VFS.??? Right there: http://lxr.linux.no/source/fs/read_write.c#L237. 222 ssize_t vfs_read(struct file *file, char __user *buf, size_t count, loff_t *pos) [...] 237 if (file->f_op->read) 238 ret = file->f_op->read(file, buf, count, pos); Sincerly, Thomas -- Thomas Petazzoni thomas.petazzoni@xxxxxxxx -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
