On Fri, 2006-01-06 at 22:34 +0530, prasad Musale wrote: > Hello , > Generic_file_read() reads from cached pages. That means the file > pages r already in page cache. But if I want to read file from disk, > How these pages comes in page cache. Ext2 & vfat call this > generic_file_read() as their read operation. I analyzed the sys_read() > code but didn't get how file is read from disk. Can anyone tell me > about that? > Thanks. For normal cases of read, generic_file_read() eventually calls do_generic_mapping_read(). It first attempts to read from the cache - this is logical. So you can see that if it finds the page and it is up to date, it is done. Otherwise, it calls the readpage function pointer (mapping->a_ops->readpage). This is a function that a file system implements to read a page from disk. Since you mentioned ext2, you can look at ext2's readpage method, called ext2_readpage(), to see how exactly the page is read from disk. Hope that is enough detail to get you started. Avishay Traeger http://www.fsl.cs.sunysb.edu/~avishay/ > > > From, > Prasad -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
