Thanks for the reply. Just one more question: what is ext2_read? I don't find a definition of ext2_read in Linux v2.6.29. The only thing I found is ext2_readpage, but apparently, it's not what you meant. Best regards, Zheng Da On 10-6-3 下午2:45, nidhi mittal hada wrote: > see as > it happens like that > > read--> sys_read--->vfs_read-->ext2_read--->readpage func of address > space ---> mpage_readpage ---> > then page is converted to single or multiple bios (depending upon > whether buffers > contained in page are physically contiguous or not ) > ---> for each buffer in page a bio is initialized ---> then submit_bio ---> > > Now > the portion highlighted is one > where page cache is consulted ---> if page is available in page cache > and uptodate too --- then no need to read from disk > otherwise ---- > process continues till submit_bio > > > now > > you need to know now > how Buffer in a page is mapped to a bio ----> there is one to one fields > are mapped .......thats given beautifully in UTLK. > > hope it clears ur doubts > Nidhi > > > > > > > > > > > On Wed, Jun 2, 2010 at 9:32 AM, Da Zheng <zhengda1936@xxxxxxxxx > <mailto:zhengda1936@xxxxxxxxx>> wrote: > > On 10-6-1 上午11:23, Joel Fernandes wrote: > >> I'm learning block devices in Linux. It seems submit_bio can be > used by file > >> systems to submit block IO requests. But after I search for it in > the linux > >> kernel, I didn't see file systems like ext2 and ext3 use it. So > how does a file > >> system usually submit a request? I didn't find a wrapper of > submit_bio or > >> generic_make_request can be used either. > > > > Usually one of the functions defined in buffer_head.h like > sb_bread or sb_getblk > > is used. The bio structure and its attributes have to be > initialized properly and > > you usually don't need to do this on your own. > Thanks. So the disk cache actually works beneath the file system > instead of on > the top of it as described in Understanding the Linux Kernel. > > Zheng Da > > -- > To unsubscribe from this list: send an email with > "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx > <mailto:ecartis@xxxxxxxxxxxx> > Please read the FAQ at http://kernelnewbies.org/FAQ > > > > > -- > Thanks & Regards > Nidhi Mittal Hada > Scientific officer D > Computer Division > Bhabha Atomic Research Center > Mumbai > > -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
