On Fri, Sep 12, 2014 at 01:35:51PM -0400, Theodore Ts'o wrote: > On Thu, Sep 11, 2014 at 03:34:47PM -0700, Darrick J. Wong wrote: > > > Hmm... I wonder if we can get away with changing ext2fs_new_block2(fs, > > > goal, bmap, ret_blk) so that if bmap is NULL, we change its behavior > > > so that (a) it tries to use the get_alloc_block() hook if it is present, and > > > (b) it will try to load the block bitmap if it is not already loaded, > > > instead of returning an error. > > > > Quite probably. I tried to avoid API behavioral change, at least for the > > inital patch, though I was thinking that a general cleanup was probably in > > order. > > It turns out that making a behavioral change could very well break > some callers --- including e2fsck (see e2fsck_get_alloc_block for an > example of wahy). What I'm currently thinking about is an API sort of > like this: I currently patched that the stupid way -- by temporarily swapping fs->get_alloc_block with NULL in new_block2() while we call the function pointer. (Also by fixing e2fsck.) > errcode_t ext2fs_alloc_blocks(ext2_filsys fs, blk64_t goal, > unsigned int *num_blocks, > char *block_buf, int flags, blk64_t *ret) > > ... which can be used to efficiently allocate up to *num_blocks blocks > at a time, much like the mballoc interface. I suspect that would be > useful for a number of different cases, including ext2fs_fallocate and > mk_hugefiles.c. Sounds familiar: http://marc.info/?l=linux-ext4&m=139898612510491&w=2 > What I'm currently wondering about is whether it's worth the interface > complexity to have something like a "struct ext2fs_allocation_request" > structure, so we can potentially add more hints that a future > implementation might use, or whether that's not worth it. > > What do folks think? I'm not sure changing a struct vs. changing whatever parameters we feed into that function is all that much different. I guess you could get around structure size changes by forcing callers to use a library allocator function. But OTOH large allocations are probably rare. --D > > - Ted > -- > 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 -- 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
