On 1/6/06, Dhaval Shirsath <dhavalrs@xxxxxxxxx> wrote: > Hi, > can anybody tell about the following 2 Q's: > > 1] What does the generic_file_read() fn does & what is the role of > the structure "stuct kiocb" ,what is its use? > generic_file_read is the generic function for file-systems which can use page cache directly and it actually creates/initializes the necesaary variables for performing read operation, do check for direct_io case and so direct_io if it is set else perform normal read operation, perform read_ahead (if required, and call readpages function of address_space_operations related to file (assigned to filp->mapping->a_ops by the file system at the time of file creation or might be in lookup) to perform the actual read from the storage and then cached those pages and provide data in the user buffer) and if data/page is not in cache then it calls the readpage function of the file-system to perform actual reading from the storage. See the generic_file_read code found in mm/filemap.c file for more detail .... The kiocb is used to do asynchronous io (seach google for more detail) > 2]What does the generic_file_open() fn does ? > generic_file_open function (what I can get by looking at the code is) just checks for the O_LARGEFILE flags in filp->flags that it will be set and the file size (getting it from inode) not greater than MAX_NON_LFS (which is (1UL<<31) -1 = 2GB) then it allow by returning 0 to open the file else it simple gives error of file is big .... (CMIIW) -- Fawad Lateef -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
