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Re: [Qemu-devel] [PATCH v2] block/gluster: add support for SEEK_DATA/SEE
From: |
Jeff Cody |
Subject: |
Re: [Qemu-devel] [PATCH v2] block/gluster: add support for SEEK_DATA/SEEK_HOLE |
Date: |
Wed, 9 Mar 2016 10:46:02 -0500 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Wed, Mar 09, 2016 at 01:30:14PM +0100, Niels de Vos wrote:
> GlusterFS 3.8 contains support for SEEK_DATA and SEEK_HOLE. This makes
> it possible to detect sparse areas in files.
>
> Signed-off-by: Niels de Vos <address@hidden>
>
> ---
> Tested by compiling and running "qemu-img map gluster://..." with a
> build of the current master branch of glusterfs. Using a Fedora cloud
> image (in raw format) shows many SEEK procudure calls going back and
> forth over the network. The output of "qemu map" matches the output when
> run against the image on the local filesystem.
>
> v2 based on feedback from Jeff Cody:
> - Replace compile time detection by runtime detection
> - Update return pointer (new argument) for .bdrv_co_get_block_status
> ---
> block/gluster.c | 186
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 186 insertions(+)
>
> diff --git a/block/gluster.c b/block/gluster.c
> index 65077a0..b01ab52 100644
> --- a/block/gluster.c
> +++ b/block/gluster.c
> @@ -23,6 +23,7 @@ typedef struct GlusterAIOCB {
> typedef struct BDRVGlusterState {
> struct glfs *glfs;
> struct glfs_fd *fd;
> + bool supports_seek_data;
> } BDRVGlusterState;
>
> typedef struct GlusterConf {
> @@ -286,6 +287,33 @@ static void qemu_gluster_parse_flags(int bdrv_flags, int
> *open_flags)
> }
> }
>
> +/*
> + * Do SEEK_DATA/HOLE to detect if it is functional. In order to be usable, it
> + * should return different values for the start of data and the start of a
> + * hole. There are three different cases to handle:
> + *
> + * - the same position is returned for data/hole (indicates broken gfapi)
> + * - an error is returned:
> + * - ENXIO only gets returned if there is valid support on client+server
> + * - EINVAL is returned when gfapi or the server does not support it
> + */
> +static bool qemu_gluster_test_seek(struct glfs_fd *fd)
> +{
> + off_t start_data, start_hole;
> + bool supports_seek_data = false;
> +
> + start_data = glfs_lseek(fd, 0, SEEK_DATA);
> + if (start_data != -1) {
I recommend just checking if the returned value is >= 0.
> + start_hole = glfs_lseek(fd, 0, SEEK_HOLE);
> + if (start_hole != -1)
Minor formatting nit: per QEMU coding standard, all conditional
statements require brackets.
> + supports_seek_data = !(start_data == start_hole);
> + } else if (errno == ENXIO) {
This errno check for ENXIO won't catch the case if an ENXIO error
occurs in the SEEK_HOLE call.
> + supports_seek_data = true;
> + }
> +
> + return supports_seek_data;
> +}
> +
> static int qemu_gluster_open(BlockDriverState *bs, QDict *options,
> int bdrv_flags, Error **errp)
> {
> @@ -320,6 +348,8 @@ static int qemu_gluster_open(BlockDriverState *bs, QDict
> *options,
> ret = -errno;
> }
>
> + s->supports_seek_data = qemu_gluster_test_seek(s->fd);
> +
> out:
> qemu_opts_del(opts);
> qemu_gluster_gconf_free(gconf);
> @@ -677,6 +707,158 @@ static int qemu_gluster_has_zero_init(BlockDriverState
> *bs)
> return 0;
> }
>
> +/*
> + * Find allocation range in @bs around offset @start.
> + * May change underlying file descriptor's file offset.
> + * If @start is not in a hole, store @start in @data, and the
> + * beginning of the next hole in @hole, and return 0.
> + * If @start is in a non-trailing hole, store @start in @hole and the
> + * beginning of the next non-hole in @data, and return 0.
> + * If @start is in a trailing hole or beyond EOF, return -ENXIO.
> + * If we can't find out, return a negative errno other than -ENXIO.
> + *
> + * (Shamefully copied from raw-posix.c, only miniscule adaptions.)
> + */
> +static int find_allocation(BlockDriverState *bs, off_t start,
> + off_t *data, off_t *hole)
> +{
> + BDRVGlusterState *s = bs->opaque;
> + off_t offs;
> +
> + if (!s->supports_seek_data)
Another formatting nit: brackets needed here as well.
> + return -EINVAL;
-ENOTSUP would probably be a better fit here, but I don't care too
much, since the error code isn't passed along outside the gluster
driver.
> +
> + /*
> + * SEEK_DATA cases:
> + * D1. offs == start: start is in data
> + * D2. offs > start: start is in a hole, next data at offs
> + * D3. offs < 0, errno = ENXIO: either start is in a trailing hole
> + * or start is beyond EOF
> + * If the latter happens, the file has been truncated behind
> + * our back since we opened it. All bets are off then.
> + * Treating like a trailing hole is simplest.
> + * D4. offs < 0, errno != ENXIO: we learned nothing
> + */
> + offs = glfs_lseek(s->fd, start, SEEK_DATA);
> + if (offs < 0) {
> + return -errno; /* D3 or D4 */
> + }
> + assert(offs >= start);
> +
> + if (offs > start) {
> + /* D2: in hole, next data at offs */
> + *hole = start;
> + *data = offs;
> + return 0;
> + }
> +
> + /* D1: in data, end not yet known */
> +
> + /*
> + * SEEK_HOLE cases:
> + * H1. offs == start: start is in a hole
> + * If this happens here, a hole has been dug behind our back
> + * since the previous lseek().
> + * H2. offs > start: either start is in data, next hole at offs,
> + * or start is in trailing hole, EOF at offs
> + * Linux treats trailing holes like any other hole: offs ==
> + * start. Solaris seeks to EOF instead: offs > start (blech).
> + * If that happens here, a hole has been dug behind our back
> + * since the previous lseek().
> + * H3. offs < 0, errno = ENXIO: start is beyond EOF
> + * If this happens, the file has been truncated behind our
> + * back since we opened it. Treat it like a trailing hole.
> + * H4. offs < 0, errno != ENXIO: we learned nothing
> + * Pretend we know nothing at all, i.e. "forget" about D1.
> + */
> + offs = glfs_lseek(s->fd, start, SEEK_HOLE);
> + if (offs < 0) {
> + return -errno; /* D1 and (H3 or H4) */
> + }
> + assert(offs >= start);
> +
> + if (offs > start) {
> + /*
> + * D1 and H2: either in data, next hole at offs, or it was in
> + * data but is now in a trailing hole. In the latter case,
> + * all bets are off. Treating it as if it there was data all
> + * the way to EOF is safe, so simply do that.
> + */
> + *data = start;
> + *hole = offs;
> + return 0;
> + }
> +
> + /* D1 and H1 */
> + return -EBUSY;
> +}
> +
> +/*
> + * Returns the allocation status of the specified sectors.
> + *
> + * If 'sector_num' is beyond the end of the disk image the return value is 0
> + * and 'pnum' is set to 0.
> + *
> + * 'pnum' is set to the number of sectors (including and immediately
> following
> + * the specified sector) that are known to be in the same
> + * allocated/unallocated state.
> + *
> + * 'nb_sectors' is the max value 'pnum' should be set to. If nb_sectors goes
> + * beyond the end of the disk image it will be clamped.
> + *
> + * (Based on raw_co_get_block_status() from raw-posix.c.)
> + */
> +static int64_t coroutine_fn qemu_gluster_co_get_block_status(
> + BlockDriverState *bs, int64_t sector_num, int nb_sectors, int *pnum,
Nit: a tab snuck in the above line, before "BlockDriverState" (tabs
expanded to spaces in coding guidelines as well).
> + BlockDriverState **file)
> +{
> + BDRVGlusterState *s = bs->opaque;
> + off_t start, data = 0, hole = 0;
> + int64_t total_size;
> + int ret = -EINVAL;
> +
> + if (!s->fd) {
> + return ret;
> + }
> +
> + start = sector_num * BDRV_SECTOR_SIZE;
> + total_size = bdrv_getlength(bs);
> + if (total_size < 0) {
> + return total_size;
> + } else if (start >= total_size) {
> + *pnum = 0;
> + return 0;
> + } else if (start + nb_sectors * BDRV_SECTOR_SIZE > total_size) {
> + nb_sectors = DIV_ROUND_UP(total_size - start, BDRV_SECTOR_SIZE);
> + }
> +
> + ret = find_allocation(bs, start, &data, &hole);
> + if (ret == -ENXIO) {
> + /* Trailing hole */
> + *pnum = nb_sectors;
> + ret = BDRV_BLOCK_ZERO;
> + } else if (ret < 0) {
> + /* No info available, so pretend there are no holes */
> + *pnum = nb_sectors;
> + ret = BDRV_BLOCK_DATA;
> + } else if (data == start) {
> + /* On a data extent, compute sectors to the end of the extent,
> + * possibly including a partial sector at EOF. */
> + *pnum = MIN(nb_sectors, DIV_ROUND_UP(hole - start,
> BDRV_SECTOR_SIZE));
> + ret = BDRV_BLOCK_DATA;
> + } else {
> + /* On a hole, compute sectors to the beginning of the next extent.
> */
> + assert(hole == start);
> + *pnum = MIN(nb_sectors, (data - start) / BDRV_SECTOR_SIZE);
> + ret = BDRV_BLOCK_ZERO;
> + }
> +
> + *file = bs;
> +
> + return ret | BDRV_BLOCK_OFFSET_VALID | start;
> +}
> +
> +
> static QemuOptsList qemu_gluster_create_opts = {
> .name = "qemu-gluster-create-opts",
> .head = QTAILQ_HEAD_INITIALIZER(qemu_gluster_create_opts.head),
> @@ -719,6 +901,7 @@ static BlockDriver bdrv_gluster = {
> #ifdef CONFIG_GLUSTERFS_ZEROFILL
> .bdrv_co_write_zeroes = qemu_gluster_co_write_zeroes,
> #endif
> + .bdrv_co_get_block_status = qemu_gluster_co_get_block_status,
> .create_opts = &qemu_gluster_create_opts,
> };
>
> @@ -746,6 +929,7 @@ static BlockDriver bdrv_gluster_tcp = {
> #ifdef CONFIG_GLUSTERFS_ZEROFILL
> .bdrv_co_write_zeroes = qemu_gluster_co_write_zeroes,
> #endif
> + .bdrv_co_get_block_status = qemu_gluster_co_get_block_status,
> .create_opts = &qemu_gluster_create_opts,
> };
>
> @@ -773,6 +957,7 @@ static BlockDriver bdrv_gluster_unix = {
> #ifdef CONFIG_GLUSTERFS_ZEROFILL
> .bdrv_co_write_zeroes = qemu_gluster_co_write_zeroes,
> #endif
> + .bdrv_co_get_block_status = qemu_gluster_co_get_block_status,
> .create_opts = &qemu_gluster_create_opts,
> };
>
> @@ -800,6 +985,7 @@ static BlockDriver bdrv_gluster_rdma = {
> #ifdef CONFIG_GLUSTERFS_ZEROFILL
> .bdrv_co_write_zeroes = qemu_gluster_co_write_zeroes,
> #endif
> + .bdrv_co_get_block_status = qemu_gluster_co_get_block_status,
> .create_opts = &qemu_gluster_create_opts,
> };
>
> --
> 2.5.0
>
- Re: [Qemu-devel] [Qemu-block] [PATCH] block/gluster: add support for SEEK_DATA/SEEK_HOLE, Eric Blake, 2016/03/07
- Re: [Qemu-devel] [Qemu-block] [PATCH] block/gluster: add support for SEEK_DATA/SEEK_HOLE, Niels de Vos, 2016/03/07
- Re: [Qemu-devel] [Qemu-block] [PATCH] block/gluster: add support for SEEK_DATA/SEEK_HOLE, Jeff Cody, 2016/03/08
- Re: [Qemu-devel] [Qemu-block] [PATCH] block/gluster: add support for SEEK_DATA/SEEK_HOLE, Niels de Vos, 2016/03/08
- [Qemu-devel] [PATCH v2] block/gluster: add support for SEEK_DATA/SEEK_HOLE, Niels de Vos, 2016/03/09
- Re: [Qemu-devel] [PATCH v2] block/gluster: add support for SEEK_DATA/SEEK_HOLE,
Jeff Cody <=
- Re: [Qemu-devel] [PATCH v2] block/gluster: add support for SEEK_DATA/SEEK_HOLE, Niels de Vos, 2016/03/09
- Re: [Qemu-devel] [PATCH v2] block/gluster: add support for SEEK_DATA/SEEK_HOLE, Jeff Cody, 2016/03/09
- [Qemu-devel] [PATCH v3] block/gluster: add support for SEEK_DATA/SEEK_HOLE, Niels de Vos, 2016/03/10
- Re: [Qemu-devel] [PATCH v3] block/gluster: add support for SEEK_DATA/SEEK_HOLE, Jeff Cody, 2016/03/15
- Re: [Qemu-devel] [PATCH v3] block/gluster: add support for SEEK_DATA/SEEK_HOLE, Jeff Cody, 2016/03/15
- Re: [Qemu-devel] [PATCH v3] block/gluster: add support for SEEK_DATA/SEEK_HOLE, Niels de Vos, 2016/03/16
Re: [Qemu-devel] [Qemu-block] [PATCH] block/gluster: add support for SEEK_DATA/SEEK_HOLE, Kevin Wolf, 2016/03/08