On Tue 04-09-07 12:01:53, Andreas Dilger wrote: > On Sep 03, 2007 20:03 +0200, Jan Kara wrote: > > I've finally got to writing up some proposal how could look system calls > > allowing for online filesystem defragmentation and generally moving file > > blocks around for improving performance. Comments are welcome. > > > > int sys_movedata(int datafd, int spacefd, loff_t from, size_t len) > > The call takes blocks used to carry data starting at offset @from of length > > @len in @spacefd and places them instead of corresponding blocks in @datafd. > > Calling these "@spacefd" and "@datafd" is a bit confusing. How about "@srcfd" > and "@tgtfd" instead? For defragmentation, are you planning to have @datafd > be the "real" inode and "@spacefd" be the temporary inode with defragged data, > or the reverse? It isn't really clear. The idea behind the names was that you move data from @datafd into blocks provided by @spacefd. Calling it @srcfd and @tgtfd has the problem whether you mean source of data or source of blocks... > > Data is copied from @datafd to newly spliced data blocks. If @spacefd contains > > a hole in the specified interval, a hole is created also in @datafd in the > > corresponding place. A data block from @spacefd and also replace a hole in > > @datafd - zeros are copied to such data block. @from and @len should be > > multiples of filesystem block size (otherwise EINVAL is returned). Data blocks > > from @datafd in the interval are released, a hole is created in @spacefd. > > This is mostly clear except the last sentence. I would think that the data > blocks in @datafd are kept, getting a copy of the data, while those in > @spacefd are released? Original blocks from @datafd are replaced by the blocks from @spacefd. So I guess you've understood the purpose of the fd's the other way around :). > > Another possibility would be to just replace data blocks without any copying > > of data (that would have to be done by the caller to before calling > > sys_movedata()). The problem here is how to avoid data loss if someone writes > > to the file after userspace has copied the data and before sys_movedata() is > > called. > Isn't that true in any case? No, I don't think so. The call should be completely safe. The idea is that we lock the i_mutex before we start swapping data blocks and unlock it after everything is done. Maybe we could even just change the mapping information inside the buffer heads? > > ssize_t sys_allocate(int fd, int mode, loff_t goal, ssize_t len) > > Allocate new space to file @fd at offset defined by file position. Both file > > offset and @len should be a multiple of filesystem block size. The whole > > interval must not contain any allocated blocks. If the interval extends past > > EOF, the file size is changed accordingly. @mode defines a way the filesystem > > will search for blocks. @mode is a bitwise OR of the following flags: > > ALLOC_FIXED_START - allocation must start at @goal; if not specified, @goal > > is just a hint where to start an allocation > > ALLOC_FIXED_LEN - allocate exactly space for @len; if not specified, upto > > @len bytes may be allocated. > > ALLOC_CONTINGUOUS - allocation must be one continguous run of blocks > > How is this much different than sys_fallocate()? It's not much different. The point is we'd like to have a better control of where and how the data is really allocated (for example to be able to create a non-linear file layout). And that is impossible with fallocate interface AFAIK... > > int sys_get_free_blocks(const char *fs, loff_t start, loff_t end, int count, > > struct alloc_extent *space) > > One alternate possibility is to call the proposed FIEMAP on the block device, > to return lists of free/used extents? We have a version of that patch for > ext4 and integration into filefrag, so it would be nice to avoid making up > yet another API/tool if that one is sufficient. Yes, that would be sufficient and looks like a good plan :). BTW: shouldn't we make it a syscall rather than ioctl? IMHO it would look much cleaner. Honza -- Jan Kara <jack@xxxxxxx> SuSE CR Labs - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
