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SubjectRe: Why side-effects on open(2) are evil. (was Re: [RFD w/info-PATCH]device arguments from lookup)
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."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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