Thank you Prasanna for info on generic_file_read. I knew that this function is used by generally all filesystems, but didn't know much about it functionality. That actor routine (which copies pages to process address space) is file_read_actor. cheers, -Manu On Thu, 30 Sep 2004 04:49:09 -0700 (PDT), prasanna wakhare <prasannawakhare@xxxxxxxxx> wrote: > Hi, > Its wrong that generic_file_read does nothing but its > very cruicial one,its allocates the page if it's not > in the cache,means some process already read that > porrtion of file and page is there in cache other wise > it repeatedly calls readpage which is cruicial and > internal to filesystem which is what implemented in > yr mentioned filesystem or ext2 and ext3, > whcih internally fills the buffers in page with the > data I.E content of that file and then returns to VFS > I.E generic_read_file, > Its time to action of generic_file_read which is very > cruicial it forward the f_pos to read next page full > of data as it repetedly calls readpage and the > routiene > i dont reming its name some --Actor routitne passes > this data to user space from kernel memory, > so taht process reading the contects of file get into > its buffer. > If i missed something please sorry for that. > > Think VFS as generic abstract Class with lots of pure > virtual functions . > And as FS developer yr filesystem is object of that > class which implements all these virtual functions as > i discussed above readpage. > > Thanks > Prasanna > > > > --- Manu Garg <manugarg@xxxxxxxxx> wrote: > > > When a special file is opened, it's file operations > > are set by > > filesystem in which the file is. Say for example if > > you have /dev/hda > > in ext3 filesystem, it's file operations will be set > > by ext3 when > > incore inode will be created (generally when file is > > opened for the > > first time). These file operation are specific to > > the file type > > (directories, link, device...etc). Now for a block > > device which > > /dev/hda is, these operations are defined in > > def_blk_fops > > (fs/block_dev.c). This structure has > > generic_file_read as it's read > > function. > > > > generic_file_read doesn't do nothing. This function > > is used for all > > filesystems that can use page_cache directly. I > > don't understand this > > function much, so cann't explain it further. > > > > Cheers! > > -Manu > > > > > > > > > > On Wed, 29 Sep 2004 15:23:24 +0545, manish regmi > > <regmi.manish@xxxxxxxxx> wrote: > > > Hi, > > > Can anybody explain me how read operation on > > Block device (say ide > > > device) work. > > > The read file operations of Block device is set to > > generic_file_read, > > > i.e nothing. and the ide driver does not have read > > routine. > > > Then, How Block device driver or Ide Driver reads > > the data? > > > > > > for eg in this type of app. > > > i = open(/dev/hda, O_RDONLY); > > > read(i ,....); > > > > > > Thanks in advance. > > > > > > -- > > > Kernelnewbies: Help each other learn about the > > Linux kernel. > > > Archive: > > http://mail.nl.linux.org/kernelnewbies/ > > > FAQ: http://kernelnewbies.org/faq/ > > > > > > > > > > > > > > -- > > ---------------- > > Manu Garg > > http://manugarg.freezope.org > > > > -- > > Kernelnewbies: Help each other learn about the Linux > > kernel. > > Archive: > > http://mail.nl.linux.org/kernelnewbies/ > > FAQ: http://kernelnewbies.org/faq/ > > > > > > > __________________________________ > Do you Yahoo!? > Yahoo! Mail is new and improved - Check it out! > http://promotions.yahoo.com/new_mail > -- ---------------- Manu Garg http://manugarg.freezope.org -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
