Hi, Dmitry, Dmitry Kasatkin <d.kasatkin@xxxxxxxxxxx> writes: > Hi, > > We are looking for advice on reading files opened for direct_io. [snip] > 2. Temporarily clear O_DIRECT in file->f_flags. [snip] > 3. Open another instance of the file with 'dentry_open' [snip] > Is temporarily clearing O_DIRECT flag really unacceptable or not? It's acceptable. However, what you're proposing to do is read the entire file into the page cache to calculate your checksum. Then, when the application goes to read the file using O_DIRECT, it will ignore the cached copy and re-read the portions of the file it wants from disk. So yes, you can do that, but it's not going to be fast. If you want to avoid polluting the cache, you can call invalidate_inode_pages2_range after you're done calculating your checksum. > Or may be there is a way to allocate "special" user-space like buffer > for kernel and use it with O_DIRECT? In-kernel O_DIRECT support has been proposed in the past, but there is no solution for that yet. Cheers, Jeff -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>