Am Mi, 2003-07-23 um 01.17 schrieb Christophe Saout: > Well, a /dev/zero-like target is very easy (attached). Damn... -- Christophe Saout <christophe@xxxxxxxx> Please avoid sending me Word or PowerPoint attachments. See http://www.fsf.org/philosophy/no-word-attachments.html
/* * Copyright (C) 2001 Sistina Software (UK) Limited. * * This file is released under the GPL. */ #include "dm.h" #include <linux/module.h> #include <linux/init.h> #include <linux/bio.h> /* * Returns the minimum that is _not_ zero, unless both are zero. */ #define min_not_zero(l, r) (l == 0) ? r : ((r == 0) ? l : min(l, r)) /* * Combine the io_restrictions with the default restrictions */ static void combine_default_restrictions(struct io_restrictions *rs) { rs->max_sectors = min_not_zero(rs->max_sectors, (unsigned short)MAX_SECTORS); rs->max_phys_segments = min_not_zero(rs->max_phys_segments, (unsigned short)MAX_PHYS_SEGMENTS); rs->max_hw_segments = min_not_zero(rs->max_hw_segments, (unsigned short)MAX_HW_SEGMENTS); rs->hardsect_size = max(rs->hardsect_size, (unsigned short)(1 << SECTOR_SHIFT)); rs->max_segment_size = min_not_zero(rs->max_segment_size, (unsigned int)MAX_SEGMENT_SIZE); rs->seg_boundary_mask = min_not_zero(rs->seg_boundary_mask, (unsigned long)0xffffffff); } /* * Construct a dummy mapping that only returns zeroes */ static int zero_ctr(struct dm_target *ti, unsigned int argc, char **argv) { if (argc != 0) { ti->error = "dm-zero: No arguments required"; return -EINVAL; } /* * FIXME: Since we don't call dm_get_device, we * have to combine the device limits ourself */ combine_default_restrictions(&ti->limits); return 0; } /* * Fills the bio pages with zeroes */ static void zero_fill_bio(struct bio *bio) { unsigned long flags; struct bio_vec *bv; int i; bio_for_each_segment(bv, bio, i) { char *data = bvec_kmap_irq(bv, &flags); memset(data, 0, bv->bv_len); bvec_kunmap_irq(bv, &flags); } } /* * Return zeroes only on reads */ static int zero_map(struct dm_target *ti, struct bio *bio, union map_info *map_context) { switch(bio_rw(bio)) { case READ: zero_fill_bio(bio); break; case READA: /* readahead of null bytes only wastes buffer cache */ return -EIO; case WRITE: /* writes get silently dropped */ break; } bio_endio(bio, bio->bi_size, 0); /* accepted bio, don't make new request */ return 0; } static struct target_type zero_target = { .name = "zero", .module = THIS_MODULE, .ctr = zero_ctr, .map = zero_map, }; int __init dm_zero_init(void) { int r = dm_register_target(&zero_target); if (r < 0) DMERR("zero: register failed %d", r); return r; } void dm_zero_exit(void) { int r = dm_unregister_target(&zero_target); if (r < 0) DMERR("zero: unregister failed %d", r); } /* * module hooks */ module_init(dm_zero_init) module_exit(dm_zero_exit) MODULE_AUTHOR("Christophe Saout <christophe@xxxxxxxx>"); MODULE_DESCRIPTION(DM_NAME " dummy target returning zeroes"); MODULE_LICENSE("GPL");