Linus Torvalds wrote:
> There are some strong arguments that we should have filesystem
> "backdoors" for maintenance purposes, including backup.
I think I agree with something Al said over IRC, that fs-level snapshots
are preferred over block level snapshots.
fs-level snapshots should become easy if you have a generic transaction
layer. The OS spits out file ops, which get processed into a set of fs
transactions. (remember that fs-level stuff like "change this block
bitmap" is also a transaction, just like the more generic "update this
inode's mtime")
Also, I think there should be generic block allocation strategies that
fs's can use. Implementing fs-specific strategies such as ext2's
readahead or XFS's delayed allocation is not a solution, IMHO, but
working towards solving the real problem.
</ramble>
> You can, of course, so parts of this on a LVM level, and doing backups
> with "disk snapshots" may be a valid approach. However, even that is
> debatable: there is very little that says that the disk image has to be
> up-to-date at any particular point in time, so even with a disk snapshot
> capability (which is not necessarily reasonable under all circumstances)
> there are arguments for maintenance interfaces.
I've been hacking on the attached, a snapshot block device driver, which
doesn't require LVM at all. (warning: compiled and updated per outside
review, but very alpha... do not apply)
The point of the driver is to provide a sync point at snapshot time, at
which all metadata and data is flushed to the block device.
My question... is there a fundamental flaw in this plan? Ideally when
userspace says "start snapshot", the fsync_dev occurs [a
simplification]. At that point, userspace can safely run dump or tar or
whatever on the virtual snapshot device.
-- Jeff Garzik | "Do you have to make light of everything?!" Building 1024 | "I'm extremely serious about nailing your MandrakeSoft | step-daughter, but other than that, yes." --------------5DC60E00EC3EAE4FA814E478 Content-Type: text/plain; charset=us-ascii; name="snap.patch" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="snap.patch"Index: linux_2_4/drivers/block/Config.in diff -u linux_2_4/drivers/block/Config.in:1.1.1.44 linux_2_4/drivers/block/Config.in:1.1.1.44.4.1 --- linux_2_4/drivers/block/Config.in:1.1.1.44 Tue May 15 04:43:24 2001 +++ linux_2_4/drivers/block/Config.in Wed May 16 15:44:59 2001 @@ -46,4 +46,6 @@ fi dep_bool ' Initial RAM disk (initrd) support' CONFIG_BLK_DEV_INITRD $CONFIG_BLK_DEV_RAM +tristate 'Snapshot device support' CONFIG_BLK_DEV_SNAP + endmenu Index: linux_2_4/drivers/block/Makefile diff -u linux_2_4/drivers/block/Makefile:1.1.1.46 linux_2_4/drivers/block/Makefile:1.1.1.46.4.1 --- linux_2_4/drivers/block/Makefile:1.1.1.46 Tue May 15 04:43:24 2001 +++ linux_2_4/drivers/block/Makefile Wed May 16 15:44:59 2001 @@ -31,6 +31,7 @@ obj-$(CONFIG_BLK_DEV_DAC960) += DAC960.o obj-$(CONFIG_BLK_DEV_NBD) += nbd.o +obj-$(CONFIG_BLK_DEV_SNAP) += snap.o subdir-$(CONFIG_PARIDE) += paride Index: linux_2_4/drivers/block/snap.c diff -u /dev/null linux_2_4/drivers/block/snap.c:1.1.6.10 --- /dev/null Sat May 19 17:36:30 2001 +++ linux_2_4/drivers/block/snap.c Thu May 17 11:48:54 2001 @@ -0,0 +1,1055 @@ +/* + Copyright 2001 Jeff Garzik <jgarzik@mandrakesoft.com> + Copyright (C) 2000 Jens Axboe <axboe@suse.de> + + May be copied or modified under the terms of the GNU General Public + License. See linux/COPYING for more information. + + Several ideas and some code taken from Jens Axboe's pktcdvd.c 0.0.2j. + + To-Do list: + * Write support. It's easy, and might be useful in isolated circumstances. + * Convert MAX_SNAPDEVS to a module parameter. + * Wrap use of "%" operator, to prepare for 64-bit-sized blockdevs on + 32-bit processors + + */ + +#define VERSION_CODE "v0.5.0-take6 17 May 2001 Jeff Garzik <jgarzik@mandrakesoft.com>" +#define MODNAME "snap" +#define PFX MODNAME ": " +#define MAX_SNAPDEVS 16 + +#include <linux/module.h> +#include <linux/kernel.h> +#include <linux/slab.h> +#include <linux/errno.h> +#include <linux/spinlock.h> +#include <linux/interrupt.h> +#include <linux/file.h> +#include <linux/blk.h> +#include <linux/blkpg.h> +#include <linux/init.h> +#include <linux/snap.h> +#include <asm/uaccess.h> + +static int *snap_sizes; +static int *snap_blksize; +static int *snap_readahead; +static struct snap_device *snap_devs; +static int snap_major = -1; +static spinlock_t snap_lock = SPIN_LOCK_UNLOCKED; + + +/* + * a bit of a kludge, but we want to be able to pass source, log, + * or snap dev and get the right one. + */ +static struct snap_device *snap_find_dev(kdev_t dev) +{ + int i, j; + struct snap_device *sd; + + spin_lock(&snap_lock); + + for (i = 0; i < MAX_SNAPDEVS; i++) { + sd = &snap_devs[i]; + if ((sd->src.dev == dev) || (sd->snap_dev == dev)) + goto out; + for (j = 0; j < sd->n_logs; j++) + if (sd->logs[j].dev == dev) + goto out; + } + sd = NULL; + +out: + spin_unlock(&snap_lock); + return sd; +} + +static request_queue_t *snap_get_queue(kdev_t dev) +{ + struct snap_device *sd = snap_find_dev(dev); + + if (!sd) + return NULL; + return &sd->q; +} + +/* run through the block bitmap on each log device, + * checking the most recently appended log first, + * to see if the requested block has been remapped and stored + * on a log device. + * If block was remapped, return log device index + */ +static int snap_find_blk(struct snap_device *sd, unsigned long blocknr) +{ + unsigned int i; + + for (i = sd->active_logs - 1; i >= 0; i--) { + unsigned long bitmap_blk = blocknr / sd->bits_per_block; + unsigned int bitmap_bits = blocknr % sd->bits_per_block; + struct buffer_head *bit_bh = bread(sd->src.dev, bitmap_blk, sd->blksz); + u8 *buf; + unsigned int in_log; + if (!bit_bh) { + printk(KERN_ERR "%s: cannot read log %u bitmap_blk %lu\n", + sd->name, i, bitmap_blk); + return -2; + } + lock_buffer(bit_bh); + buf = bit_bh->b_data; + in_log = (buf[bitmap_bits / sizeof(u8)] & (1 << (bitmap_bits % sizeof(u8)))); + unlock_buffer(bit_bh); + brelse(bit_bh); + if (in_log) + return i; + } + + return -1; +} + +/* we have never stored a block located at src_bh->b_rsector before. + * allocate space on a log device, and store it. + */ +static int snapshot_blk(struct snap_device *sd, request_queue_t *q, + struct buffer_head *src_bh) +{ + unsigned int log; + struct buffer_head old_bh_d; + struct buffer_head *old_bh = &old_bh_d; + struct buffer_head *bit_bh, *map_bh, *data_bh; + unsigned long bitmap_blk, map_blk, data_blk; + unsigned int bitmap_bits, map_ofs; + unsigned long blocknr = src_bh->b_rsector; + unsigned long *map; + u8 *buf; + + /* get index of last active log */ + if (sd->active_logs == 0) { + log = 0; + sd->active_logs++; + } else { + log = sd->active_logs - 1; + } + + /* if no free blocks in current log, move on to the next log. */ + if (sd->logs[log].free == 0) { + + /* if no more logs, end snapshot */ + if (sd->active_logs == sd->n_logs) { + request_queue_t *sq = sd->src.q; + spin_lock_irq(&io_request_lock); + + sq->make_request_fn = sd->src.make_request_fn; + sd->src.make_request_fn = NULL; + clear_bit(SNAP_ACTIVE, &sd->flags); + + spin_unlock_irq(&io_request_lock); + printk(KERN_WARNING "%s: device full, ending snapshot\n", sd->name); + return q->make_request_fn(q, WRITE, src_bh); + } + + sd->active_logs++; + log++; + } + + /* read old data from source device */ + /* call ll_rw_blk directly on a custom bh to avoid some conflicts */ + init_buffer(old_bh, NULL, NULL); + atomic_set(&old_bh->b_count, 1); + old_bh->b_rdev = sd->src.dev; + old_bh->b_rsector = blocknr; + old_bh->b_state = 1 << BH_Mapped; + old_bh->b_size = sd->blksz; + old_bh->b_data = kmalloc(sd->blksz, GFP_KERNEL); + if (!old_bh->b_data) { + printk(KERN_ERR "%s: memory alloc fail on srcdev blk %lu\n", + sd->name, blocknr); + goto end_io; + } + ll_rw_block(READ, 1, &old_bh); + wait_on_buffer(old_bh); + lock_buffer(old_bh); + + /* read bitmap block from log device */ + bitmap_blk = blocknr / sd->bits_per_block; + bit_bh = bread(sd->logs[log].dev, bitmap_blk, sd->blksz); + if (!bit_bh) { + brelse(old_bh); + printk(KERN_ERR "%s: cannot read log %u bitmap_blk %lu\n", + sd->name, log, bitmap_blk); + goto end_io; + } + lock_buffer(bit_bh); + + /* read map block from log device */ + map_blk = sd->map_base + (blocknr / sd->maps_per_block); + map_bh = bread(sd->logs[log].dev, map_blk, sd->blksz); + if (!map_bh) { + brelse(old_bh); + unlock_buffer(bit_bh); + brelse(bit_bh); + printk(KERN_ERR "%s: cannot read log %u map_blk %lu\n", + sd->name, log, map_blk); + goto end_io; + } + lock_buffer(map_bh); + + /* getblk data block from log device */ + data_blk = sd->data_base + (sd->logs[log].data_blocks - sd->logs[log].free); + data_bh = getblk(sd->logs[log].dev, data_blk, sd->blksz); + if (!data_bh) { + brelse(old_bh); + unlock_buffer(bit_bh); + brelse(bit_bh); + unlock_buffer(map_bh); + brelse(map_bh); + printk(KERN_ERR "%s: cannot getblk log %u data_blk %lu\n", + sd->name, log, data_blk); + goto end_io; + } + lock_buffer(data_bh); + + /* write snapshot of source block to log device */ + memcpy(data_bh->b_data, old_bh->b_data, sd->blksz); + mark_buffer_dirty(data_bh); + mark_buffer_uptodate(data_bh, 1); + unlock_buffer(data_bh); + brelse(data_bh); + + unlock_buffer(old_bh); + brelse(old_bh); + kfree(old_bh->b_data); + + /* update block map on logdev to point to snapshot'd block */ + map_ofs = blocknr % sd->maps_per_block; + map = (unsigned long *) map_bh->b_data; + map[map_ofs] = data_blk; + mark_buffer_dirty(map_bh); + mark_buffer_uptodate(map_bh, 1); + unlock_buffer(map_bh); + brelse(map_bh); + + /* update bitmap on logdev to indicate remapped block + * is stored on this log device + */ + bitmap_bits = blocknr % sd->bits_per_block; + buf = bit_bh->b_data; + buf[bitmap_bits / sizeof(u8)] |= (1 << (bitmap_bits % sizeof(u8))); + mark_buffer_dirty(bit_bh); + mark_buffer_uptodate(bit_bh, 1); + unlock_buffer(bit_bh); + brelse(bit_bh); + + /* update free count */ + sd->logs[log].free--; + + /* finally, pass the write down to the source device */ + return sd->src.make_request_fn(q, WRITE, src_bh); + +end_io: + buffer_IO_error(src_bh); + return 0; +} + +/* + * our replacement for the source device's make_request_fn + */ +static int src_make_request(request_queue_t *q, int rw, struct buffer_head *bh) +{ + struct snap_device *sd; + int log; + + sd = snap_find_dev(bh->b_rdev); + + /* + * various sanity checks + */ + + if (sd == NULL) { + printk(KERN_ERR PFX "src request routed to us by unknown snap device\n"); + goto end_io; + } + + if (bh->b_size != sd->blksz) { + printk(KERN_ERR "%s: wrong bh size\n", sd->name); + goto end_io; + } + + /* read is easy - simply pass it on through to + * underlying block device + */ + if (rw == READ || rw == READA) + return sd->src.make_request_fn(q, rw, bh); + + /* sanity check */ + if (rw != WRITE) { + printk(KERN_ERR "%s: unknown rw mode %d\n", sd->name, rw); + goto end_io; + } + + /* if block was already remapped, let the write proceed + * as-is. No more work needs to be done on our part. + */ + log = snap_find_blk(sd, bh->b_rsector); + if (log < -1) + goto end_io; + if (log >= 0) + return sd->src.make_request_fn(q, rw, bh); + + /* block was not already remapped, write to a log device */ + return snapshot_blk(sd, q, bh); + +end_io: + buffer_IO_error(bh); + return 0; +} + +/* + * turns snapshotting on or off, AFTER the device has been set up + */ +static int snap_mode(struct snap_device *sd, unsigned int starting) +{ + request_queue_t *sq; + + if (!sd->src.q) + return -EINVAL; + if (starting && test_bit(SNAP_ACTIVE, &sd->flags)) + return -EINVAL; + if (!starting && !test_bit(SNAP_ACTIVE, &sd->flags)) + return -EINVAL; + + sd->src.q = sq = blk_get_queue(sd->src.dev); + + /* flush outstanding I/Os for the source device. + * Note that this is a race -IF- we were attempting + * to ensure no I/Os occur between call to fsync_dev() + * and when the swap make_request functions, below. + * However, we don't care about this race since this + * is just a sync point, so life is good. + */ + fsync_dev(sd->src.dev); + + /* swap srcdev make_request_fn with our own + */ + spin_lock_irq(&io_request_lock); + + if (starting) { + set_bit(SNAP_ACTIVE, &sd->flags); + sd->src.make_request_fn = sq->make_request_fn; + sq->make_request_fn = src_make_request; + } else { + sq->make_request_fn = sd->src.make_request_fn; + sd->src.make_request_fn = NULL; + clear_bit(SNAP_ACTIVE, &sd->flags); + } + + spin_unlock_irq(&io_request_lock); + + printk(KERN_INFO "%s: %sing snapshot of %s\n", + sd->name, starting ? "start" : "end", bdevname(sd->src.dev)); + + return 0; +} + +/* + * a read has occured on the snapshot blkdev, and we know + * the block has been remapped, and we know it is on log + * device 'log'. Remap the read into a read of the log device. + */ +static int remap_to_logdev(struct snap_device *sd, unsigned int log, + request_queue_t *q, int rw, struct buffer_head *bh) +{ + unsigned long map_blk; + unsigned int map_ofs; + struct buffer_head *map_bh; + unsigned long *map; + + /* + * calc the position in the vector of unsigned long + * block numbers where remapped block number is stored + */ + map_blk = sd->map_base + (bh->b_rsector / sd->maps_per_block); + map_ofs = bh->b_rsector % sd->maps_per_block; + + /* read the block from the vector */ + map_bh = bread(sd->logs[log].dev, map_blk, sd->blksz); + if (!map_bh) { + printk(KERN_ERR "%s: unable to read log %u block %lu\n", + sd->name, log, map_blk); + goto end_io; + } + lock_buffer(map_bh); + + /* read remapped block number from vector */ + map = (unsigned long *) map_bh->b_data; + map_blk = map[map_ofs]; + unlock_buffer(map_bh); + brelse(map_bh); + + /* do the remap */ + bh->b_rdev = sd->logs[log].dev; + bh->b_rsector = map_blk; + return 1; + +end_io: + buffer_IO_error(bh); + return 0; +} + +/* + * the make_request_fn for our virtual snapshot blkdev. + * All reads are remapped to the source device or a log device, + * after some I/O occurs to device where to remap the read. + * Writes are not currently supported. + */ +static int snap_make_request(request_queue_t *q, int rw, struct buffer_head *bh) +{ + struct snap_device *sd; + int log; + + if (MINOR(bh->b_rdev) >= MAX_SNAPDEVS) { + printk(KERN_ERR PFX "%s out of range\n", kdevname(bh->b_rdev)); + goto end_io; + } + + sd = &snap_devs[MINOR(bh->b_rdev)]; + + /* + * various sanity checks + */ + + if (!sd->src.dev) { + printk(KERN_ERR "%s: request received for non-active sd\n", sd->name); + goto end_io; + } + + if (rw != READ && rw != READA) { + printk(KERN_ERR "%s: non-READ[A] request\n", sd->name); + goto end_io; + } + + if (bh->b_size != sd->blksz) { + printk(KERN_ERR "%s: wrong bh size\n", sd->name); + goto end_io; + } + + log = snap_find_blk(sd, bh->b_rsector); + if (log < -1) + goto end_io; + if (log >= 0) + return remap_to_logdev(sd, log, q, rw, bh); + + /* + * ok, the block was not remapped onto a log device, + * so remap the request to request from the original + * source device. Since block numbers are the same + * on the virtual snapdev and the srcdev, we need + * only to change the device to which the read request + * is targetted. + */ + bh->b_rdev = sd->src.dev; + return 1; + +end_io: + buffer_IO_error(bh); + return 0; +} + +/* + * initialize the request queue for the snapshot blkdev + */ +static void snap_init_queue(struct snap_device *sd) +{ + request_queue_t *q = &sd->q; + + blk_queue_make_request(q, snap_make_request); + blk_queue_headactive(q, 0); +} + +/********************************************************************** + * + * Block device ioctl operation and associated functions. + * + */ + +/* initialize a log device. all we need to do is zero the bitmap + * that appears at the beginning of the disk + */ +static void snap_mkfs (struct snap_device *sd, unsigned int logidx, + unsigned int bitmap_blocks) +{ + unsigned int i, blksz = sd->blksz; + + for (i = 0; i < bitmap_blocks; i++) { + struct buffer_head *bh = getblk(sd->logs[i].dev, i, blksz); + if (bh) { + lock_buffer(bh); + memset(bh->b_data, 0, blksz); + mark_buffer_dirty(bh); + mark_buffer_uptodate(bh, 1); + unlock_buffer(bh); + brelse(bh); + } else { + printk(KERN_ERR "%s: cannot get blk %u\n", sd->name, i); + } + } +} + +/* + * the source and log devices have been opened and sanity-checked + * at this point. initialize 'sd' based on the information provided + */ +static int snap_new_dev(struct snap_device *sd, + kdev_t src_dev, struct block_device *src_bdev, + unsigned int n_log_fds, struct snap_dev_init_info *sdii) +{ + unsigned int i; + unsigned long map_blocks, bitmap_blocks; + int ret; + void *log_buf; + + MOD_INC_USE_COUNT; + + log_buf = kmalloc(sizeof(struct snap_log) * n_log_fds, GFP_KERNEL); + if (!log_buf) { + ret = -ENOMEM; + goto out_bufs; + } + + spin_lock(&snap_lock); + + memset(sd, 0, sizeof(struct snap_device)); + + sd->src.dev = src_dev; + sd->src.q = blk_get_queue (sd->src.dev); + sd->blksz = blksize_size[MAJOR(src_dev)][MINOR(src_dev)]; + sd->src.bdev = src_bdev; + sd->src.blocks = blk_size[MAJOR(src_dev)][MINOR(src_dev)]; + + sd->n_logs = n_log_fds; + sd->logs = log_buf; + memset(sd->logs, 0, sizeof(struct snap_log) * n_log_fds); + + sd->bits_per_block = sd->blksz * 8; + sd->maps_per_block = sd->blksz / (sizeof(unsigned long) * 2); + + bitmap_blocks = sd->src.blocks / sd->bits_per_block; + if (sd->src.blocks % sd->bits_per_block) + bitmap_blocks++; + + map_blocks = sd->src.blocks / sd->maps_per_block; + if (sd->src.blocks % sd->maps_per_block) + map_blocks++; + + sd->map_base = bitmap_blocks; + sd->data_base = bitmap_blocks + map_blocks; + + for (i = 0; i < n_log_fds; i++) { + kdev_t logdev = sdii[i].inode->i_rdev; + sd->logs[i].dev = logdev; + sd->logs[i].size = blk_size[MAJOR(logdev)][MINOR(logdev)]; + + if (sd->logs[i].size < (sd->data_base * 2)) { + ret = -EINVAL; + goto out_free; + } + + sd->logs[i].data_blocks = + sd->logs[i].free = + sd->logs[i].size - bitmap_blocks - map_blocks; + + set_blocksize(logdev, sd->blksz); + } + + sd->snap_dev = MKDEV(snap_major, i); + sprintf(sd->name, "snap%d", i); + atomic_set(&sd->refcnt, 0); + + spin_unlock(&snap_lock); + + snap_init_queue(sd); + + for (i = 0; i < n_log_fds; i++) + snap_mkfs (sd, i, bitmap_blocks); + + DPRINTK(PFX "dev %s sucessfully registered\n", sd->name); + return 0; + +out_free: + spin_unlock(&snap_lock); + kfree(sd->logs); +out_bufs: + MOD_DEC_USE_COUNT; + return ret; +} + +/* clean up in the event of snap_setup_dev error exit */ +static void snap_setup_dev_cleanup (unsigned int n_log_fds, struct file *src, + struct snap_dev_init_info *sdii) +{ + unsigned int i; + + if (sdii) { + for (i = 0; i < n_log_fds; i++) + if (sdii[i].file) { + blkdev_put(sdii[i].inode->i_bdev, BDEV_FILE); + fput(sdii[i].file); + } + kfree(sdii); + } + + if (src) { + blkdev_put(src->f_dentry->d_inode->i_bdev, BDEV_FILE); + fput(src); + } +} + +/* + * called from ioctl. verifies the passed file descriptors to + * be open and valid block devices, then called snap_new_dev + * to actually initialize the device + */ +static int snap_setup_dev(struct snap_device *sd, struct snap_setup *setup) +{ + struct snap_dev_init_info *sdii = NULL; + struct inode *inode_src; + struct file *src; + int ret; + unsigned int i, n_log_fds = setup->n_log_fds; + + if ((src = fget(setup->src_fd)) == NULL) { + printk(KERN_ERR "%s: bad file descriptor %d passed\n", sd->name, setup->src_fd); + return -EBADF; + } + if ((inode_src = src->f_dentry->d_inode) == NULL) { + printk(PFX "huh? file descriptor %d contains no inode?\n", setup->src_fd); + fput(src); + return -EINVAL; + } + if (!S_ISBLK(inode_src->i_mode)) { + printk(PFX "device is not a block device (duh)\n"); + fput(src); + return -ENOTBLK; + } + if (snap_find_dev(inode_src->i_rdev)) { + printk(PFX "source device associated with another snapshot dev\n"); + fput(src); + return -EBUSY; + } + ret = blkdev_get(inode_src->i_bdev, src->f_mode, src->f_flags, BDEV_FILE); + if (ret) { + fput(src); + return ret; + } + + sdii = kmalloc(sizeof(*sdii) * n_log_fds, GFP_KERNEL); + if (!sdii) { + ret = -ENOMEM; + goto out; + } + memset(sdii, 0, sizeof(*sdii) * n_log_fds); + + for (i = 0; i < n_log_fds; i++) { + struct file *logf; + struct inode *logi; + + logf = sdii[i].file = fget(setup->log_fd[i]); + if (!logf) { + printk(PFX "bad file descriptor %d passed\n", + setup->log_fd[i]); + ret = -EBADF; + goto out; + } + logi = sdii[i].inode = sdii[i].file->f_dentry->d_inode; + if (!logi) { + printk(PFX "huh? file descriptor %d contains no inode?\n", + setup->log_fd[i]); + ret = -EINVAL; + goto out; + } + if (!S_ISBLK(logi->i_mode)) { + printk(PFX "device is not a block device\n"); + ret = -ENOTBLK; + goto out; + } + if (snap_find_dev(logi->i_rdev)) { + printk(PFX "log device %d associated with another snapshot dev\n", i); + ret = -EBUSY; + goto out; + } + if (IS_RDONLY(logi)) { + printk(PFX "Can't write to read-only dev\n"); + ret = -EROFS; + goto out; + } + ret = blkdev_get(logi->i_bdev, logf->f_mode, + logf->f_flags, BDEV_FILE); + if (ret) + goto out; + } + + if ((ret = snap_new_dev(sd, inode_src->i_rdev, inode_src->i_bdev, + n_log_fds, sdii))) { + printk(PFX "all booked up\n"); + goto out; + } + + sd->src.dentry = dget(src->f_dentry); + for (i = 0; i < n_log_fds; i++) + sd->logs[i].dentry = dget(sdii[i].file->f_dentry); + atomic_inc(&sd->refcnt); + + ret = 0; +out: + snap_setup_dev_cleanup(n_log_fds, src, sdii); + return ret; +} + +/* + * called from ioctl. tears down the currently + * setup snapshot device, and closes all open resources + */ +static int snap_remove_dev(struct snap_device *sd) +{ + unsigned int i; + + /* terminate any on-going snapshot, if any */ + snap_mode(sd, 0); + + blkdev_put(sd->src.dentry->d_inode->i_bdev, BDEV_FILE); + dput(sd->src.dentry); + + for (i = 0; i < sd->n_logs; i++) { + blkdev_put(sd->logs[i].dentry->d_inode->i_bdev, BDEV_FILE); + dput(sd->logs[i].dentry); + invalidate_buffers(sd->logs[i].dev); + } + kfree(sd->logs); + + invalidate_buffers(sd->snap_dev); + + for (i = 0; i < sd->n_logs; i++) + blk_cleanup_queue(blk_get_queue(sd->logs[i].dev)); + blk_cleanup_queue(blk_get_queue(sd->src.dev)); + + DPRINTK(PFX "dev %s unregistered\n", sd->name); + + memset(sd, 0, sizeof(struct snap_device)); + + MOD_DEC_USE_COUNT; + return 0; +} + +static int snap_ioctl(struct inode *inode, struct file *file, + unsigned int cmd, unsigned long arg) +{ + struct snap_device *sd; + int err; + + if (MINOR(inode->i_rdev) >= MAX_SNAPDEVS) + return -EINVAL; + + sd = &snap_devs[MINOR(inode->i_rdev)]; + + if ((cmd != SNAP_SETUP_DEV) && !sd->src.dev) { + DPRINTK(PFX "dev not setup\n"); + return -ENXIO; + } + + switch (cmd) { + case SNAP_GET_STATS: + if (copy_to_user(&arg, &sd->stats, sizeof(struct snap_stats))) + return -EFAULT; + + case SNAP_SETUP_DEV: { + struct snap_setup se, *sp; + unsigned int alloc_size; + + if (!capable(CAP_SYS_ADMIN)) + return -EPERM; + if (sd->src.dev) { + printk(PFX "dev already setup\n"); + return -EBUSY; + } + if (copy_from_user(&se, &arg, sizeof(se))) + return -EFAULT; + if (se.n_log_fds == 0 || se.n_log_fds > MAX_LOGDEVS) + return -EINVAL; + alloc_size = sizeof(se) + (sizeof(int) * se.n_log_fds); + sp = kmalloc(alloc_size, GFP_KERNEL); + if (!sp) + return -ENOMEM; + if (copy_from_user(sp, &arg, alloc_size)) { + kfree(sp); + return -EFAULT; + } + err = snap_setup_dev(sd, sp); + kfree(sp); + return err; + } + + case SNAP_TEARDOWN_DEV: + if (!capable(CAP_SYS_ADMIN)) + return -EPERM; + fsync_dev(sd->src.dev); /* HACK! minimize, but not close, race */ + if (atomic_read(&sd->refcnt) != 1) + return -EBUSY; + return snap_remove_dev(sd); + + case SNAP_START: + return snap_mode(sd, 1); + case SNAP_END: + return snap_mode(sd, 0); + + case BLKGETSIZE: + return put_user(blk_size[snap_major][MINOR(inode->i_rdev)] << 1, (long *)arg); + + case BLKROSET: + case BLKROGET: + case BLKSSZGET: + case BLKRASET: + case BLKRAGET: + case BLKFLSBUF: + return blk_ioctl(inode->i_rdev, cmd, arg); + + /* + * forward all other ioctls to src blkdev + */ + default: + return ioctl_by_bdev(sd->src.bdev, cmd, arg); + } + + return 0; +} + +/********************************************************************** + * + * Block device operations (open/close/check_media_change), + * and associated functions. + * + */ + +static inline void snap_mark_readonly(struct snap_device *sd, int on) +{ + if (on) + set_bit(SNAP_READONLY, &sd->flags); + else + clear_bit(SNAP_READONLY, &sd->flags); +} + +static int snap_open_dev(struct snap_device *sd, int write) +{ + unsigned long dev_size; + + if (!sd->src.dev) + return 0; + + dev_size = blk_size[MAJOR(sd->src.dev)][MINOR(sd->src.dev)]; + snap_sizes[MINOR(sd->snap_dev)] = dev_size; + + if (write) { +#if 0 /* no write support */ + if ((ret = snap_open_write(sd))) + return ret; + snap_mark_readonly(sd, 0); +#else + return -EINVAL; +#endif + } else { + snap_mark_readonly(sd, 1); + } + + if (write) + printk(PFX "%lukB available on disc\n", dev_size); + + return 0; +} + +static int snap_open(struct inode *inode, struct file *file) +{ + struct snap_device *sd = NULL; + int ret; + + VPRINTK(PFX "entering open\n"); + + /* remove when write mode is supported */ + if (file->f_mode & FMODE_WRITE) { + printk(PFX "write mode not supported\n"); + return -EINVAL; + } + + MOD_INC_USE_COUNT; + + if (MINOR(inode->i_rdev) >= MAX_SNAPDEVS) { + printk(PFX "max %d snapdevs supported\n", MAX_SNAPDEVS); + ret = -ENODEV; + goto out; + } + + /* + * either device is not configured, or pktsetup is old and doesn't + * use O_CREAT to create device + */ + sd = &snap_devs[MINOR(inode->i_rdev)]; + if (!sd->src.dev && !(file->f_flags & O_CREAT)) { + VPRINTK(PFX "not configured and O_CREAT not set\n"); + ret = -ENXIO; + goto out; + } + + atomic_inc(&sd->refcnt); + if ((atomic_read(&sd->refcnt) > 1) && (file->f_mode & FMODE_WRITE)) { + VPRINTK(PFX "busy open for write\n"); + ret = -EBUSY; + goto out_dec; + } + + ret = snap_open_dev(sd, file->f_mode & FMODE_WRITE); + if (ret) + goto out_dec; + + /* + * needed here as well, since ext2 (among others) may change + * the blocksize at mount time + */ + set_blocksize(sd->snap_dev, sd->blksz); + return 0; + +out_dec: + atomic_dec(&sd->refcnt); +out: + VPRINTK(PFX "failed open (%d)\n", ret); + MOD_DEC_USE_COUNT; + return ret; +} + +static void snap_release_dev(struct snap_device *sd) +{ + fsync_dev(sd->snap_dev); + invalidate_buffers(sd->snap_dev); + + atomic_dec(&sd->refcnt); +} + +static int snap_close(struct inode *inode, struct file *file) +{ + struct snap_device *sd = &snap_devs[MINOR(inode->i_rdev)]; + + if (sd->src.dev) + snap_release_dev(sd); + + MOD_DEC_USE_COUNT; + return 0; +} + +/* FIXME: -really- handle media change, by disabling active snapshot + * if source media changes, or handle fatal errors if target media + * changes + */ +static int snap_media_change(kdev_t dev) +{ + struct snap_device *sd = &snap_devs[MINOR(dev)]; + return sd->src.bdev->bd_op->check_media_change(dev); +} + +static struct block_device_operations snap_ops = { + open: snap_open, + release: snap_close, + ioctl: snap_ioctl, + check_media_change: snap_media_change, +}; + +/********************************************************************** + * + * Module initializations and cleanup + * + */ + +static inline void snap_cleanup (void) +{ + if (snap_devs) + kfree(snap_devs); + if (snap_sizes) + kfree(snap_sizes); + if (snap_blksize) + kfree(snap_blksize); + if (snap_readahead) + kfree(snap_readahead); + + snap_devs = NULL; + snap_sizes = NULL; + snap_blksize = NULL; + snap_readahead = NULL; + blk_size[snap_major] = NULL; + blksize_size[snap_major] = NULL; + max_readahead[snap_major] = NULL; + blk_dev[snap_major].queue = NULL; +} + +static int __init snap_init(void) +{ + snap_major = devfs_register_blkdev(0, MODNAME, &snap_ops); + if (snap_major <= 0) { /* zero is invalid value b/c we need a major */ + printk("unable to register snap device\n"); + return -EIO; + } + devfs_register(NULL, MODNAME, 0, DEVFS_FL_DEFAULT, snap_major, + S_IFBLK | S_IRUSR | S_IWUSR, &snap_ops, NULL); + + snap_sizes = kmalloc(MAX_SNAPDEVS * sizeof(int), GFP_KERNEL); + if (snap_sizes == NULL) + goto err; + + snap_blksize = kmalloc(MAX_SNAPDEVS * sizeof(int), GFP_KERNEL); + if (snap_blksize == NULL) + goto err; + + snap_readahead = kmalloc(MAX_SNAPDEVS * sizeof(int), GFP_KERNEL); + if (snap_readahead == NULL) + goto err; + + snap_devs = kmalloc(MAX_SNAPDEVS * sizeof(struct snap_device), GFP_KERNEL); + if (snap_devs == NULL) + goto err; + + memset(snap_devs, 0, MAX_SNAPDEVS * sizeof(struct snap_device)); + memset(snap_sizes, 0, MAX_SNAPDEVS * sizeof(int)); + memset(snap_blksize, 0, MAX_SNAPDEVS * sizeof(int)); + memset(snap_readahead, 0, MAX_SNAPDEVS * sizeof(int)); + + blk_size[snap_major] = snap_sizes; + blksize_size[snap_major] = snap_blksize; + max_readahead[snap_major] = snap_readahead; + read_ahead[snap_major] = 128; + + blk_dev[snap_major].queue = snap_get_queue; + + DPRINTK(PFX "%s\n", VERSION_CODE); + return 0; + +err: + printk(PFX "out of memory\n"); + devfs_unregister(devfs_find_handle(NULL, MODNAME, 0, 0, + DEVFS_SPECIAL_BLK, 0)); + devfs_unregister_blkdev(snap_major, MODNAME); + snap_cleanup (); + return -ENOMEM; +} + +static void __exit snap_exit(void) +{ + devfs_unregister(devfs_find_handle(NULL, MODNAME, 0, 0, + DEVFS_SPECIAL_BLK, 0)); + devfs_unregister_blkdev(snap_major, MODNAME); + + snap_cleanup (); + snap_major = 0; +} + +MODULE_DESCRIPTION("Snapshot block device"); +MODULE_AUTHOR("Jeff Garzik <jgarzik@mandrakesoft.com>"); + +module_init(snap_init); +module_exit(snap_exit); Index: linux_2_4/include/linux/snap.h diff -u /dev/null linux_2_4/include/linux/snap.h:1.1.6.5 --- /dev/null Sat May 19 17:36:31 2001 +++ linux_2_4/include/linux/snap.h Thu May 17 11:09:38 2001 @@ -0,0 +1,126 @@ +/* + * Copyright 2001 Jeff Garzik <jgarzik@mandrakesoft.com> + * Copyright (C) 2000 Jens Axboe <axboe@suse.de> + * + * May be copied or modified under the terms of the GNU General Public + * License. See linux/COPYING for more information. + * + */ +#ifndef __LINUX_SNAP_H +#define __LINUX_SNAP_H + +/* + * 1 for normal debug messages, 2 is very verbose. 0 to turn it off. + */ +#define SNAP_DEBUG 1 + +/* + * No user-servicable parts beyond this point -> + */ + +#if SNAP_DEBUG +#define DPRINTK(fmt, args...) printk(KERN_NOTICE fmt, ##args) +#else +#define DPRINTK(fmt, args...) +#endif + +#if SNAP_DEBUG > 1 +#define VPRINTK(fmt, args...) printk(KERN_NOTICE fmt, ##args) +#else +#define VPRINTK(fmt, args...) +#endif + +/* bh list unique identifier */ +#define SNAP_BUF_LIST 0x93 + +/* + * flags + */ +#define SNAP_READONLY 1 /* read only dev */ +#define SNAP_ACTIVE 2 /* snapshot dev is active */ + +/* + * Very unused stats for now + */ +struct snap_stats +{ + unsigned long bh_s; + unsigned long bh_e; + unsigned long bh_cache_hits; + unsigned long page_cache_hits; + unsigned long secs_w; + unsigned long secs_r; +}; + +#define MAX_LOGDEVS 512 /* arbitrary limit */ + +struct snap_setup +{ + int src_fd; + unsigned int n_log_fds; + int log_fd[0]; +}; + +/* + * packet ioctls + */ +#define SNAP_IOCTL_MAGIC ('N') +#define SNAP_GET_STATS _IOR(SNAP_IOCTL_MAGIC, 0xE0, struct snap_stats) +#define SNAP_SETUP_DEV _IOW(SNAP_IOCTL_MAGIC, 0xE1, struct snap_setup) +#define SNAP_TEARDOWN_DEV _IOW(SNAP_IOCTL_MAGIC, 0xE2, unsigned int) +#define SNAP_START _IO(SNAP_IOCTL_MAGIC, 0xE3) +#define SNAP_END _IO(SNAP_IOCTL_MAGIC, 0xE4) + +#ifdef __KERNEL__ +#include <linux/blkdev.h> + +struct snap_dev_init_info +{ + struct inode *inode; + struct file *file; +}; + +struct snap_src +{ + request_queue_t *q; + kdev_t dev; + + make_request_fn *make_request_fn; + + struct block_device *bdev; + struct dentry *dentry; + unsigned long blocks; +}; + +struct snap_log +{ + kdev_t dev; + struct dentry *dentry; + unsigned long size; + unsigned long free; + unsigned long data_blocks; +}; + +struct snap_device +{ + struct snap_src src; + struct snap_log *logs; + unsigned int n_logs; + unsigned int active_logs; + + request_queue_t q; + atomic_t refcnt; + kdev_t snap_dev; + unsigned long flags; + char name[20]; + unsigned int bits_per_block; + unsigned int maps_per_block; + unsigned long map_base; + unsigned long data_base; + unsigned int blksz; + struct snap_stats stats; +}; + +#endif /* __KERNEL__ */ + +#endif /* __LINUX_SNAP_H */
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