At the protocol level the write will require a layout and device information so that the client can map the byte offsets in the file to the particular devices. So, in case the client does not have this information in its cache it may issue a LAYOUTGET to the metadata server. This happens in _pnfs_update_layout() which is currently being called from nfs_write_begin() (which essentially happens when the application data enters the client's cache) For any new device id mentioned in the layout, the layout driver will issue a GETDEVICEINFO to populate the device cache. For example see this path: filelayout_alloc_lseg filelayout_check_layout get_device_info. Eventually, when the data is flushed onto the storage the client and layout driver use the cached layout to write and commit the data to the data servers. See for example: nfs_writepage nfs_writepage_locked nfs_pageio_init_write nfs_pageio_init(... nfs_flush_multi) nfs_flush_multi nfs_write_rpcsetup pnfs_initiate_write pnfs_try_to_write_data _pnfs_try_to_write_data pnfs_writepages nfss->pnfs_curr_ld->ld_io_ops->write_pagelist() Which is, for example in the files layout case: filelayout_write_pagelist that in turn, calls nfs_initiate_write for the data server serving the byte offset later COMMIT (or the equivalent for the particular layout driver) may be called to commit the written data to non-volatile storage and LAYOUTCOMMIT is sent to the metadata server A code path that issues this, for example, starts in nfs_write_inode I hope this helps! Benny -----Original Message----- From: quanli gui [mailto:gqlxj1987@xxxxxxxxx] Sent: Tue 2010-06-29 10:58 To: Halevy, Benny Subject: Re: [pnfs]pnfs functions procedure I means that for example, when i want to write a file, how pnfs handle this write file command? It would treat this command with which functions in pnfs. how is the functions procedure? 2010/6/29 Halevy, Benny <bhalevy@xxxxxxxxxxx> > Dear Quanli, > > I'm not sure what you meant exactly from your message > so we'll have to close the language barrier somehow. > (I'm not a native English speaker as well ;-)) > > It would help if you can please provide a concrete > example of a simple thing you want to accomplish > so we can focus on how to help you achieve that. > > Thanks, > > Benny > > -----Original Message----- > From: quanli gui [mailto:gqlxj1987@xxxxxxxxx] > Sent: Tue 2010-06-29 05:07 > To: linux-pnfs > Cc: Halevy, Benny > Subject: [pnfs]pnfs functions procedure > > For pnfs, I nearly know every function, that means that i almost know the > meanings of the function. But i don't know how to tandem these functions. > I > don't know in fact i use which function when i use pnfs. I don't know how > to > connect the function to the defacto use. When i use pnfs setup by setup, > the functions procedure? I don't know. I hope that someone can give me > something about this. Thanks. > > -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
