Re: [Qemu-devel] [PATCH v3] sheepdog: selectable object size support

[Teruaki Ishizaki]

Hi, Kevin

Thanks for your review!

(2015/01/23 22:53), Kevin Wolf wrote:
> Am 23.01.2015 um 09:24 hat Teruaki Ishizaki geschrieben:
> > Previously, qemu block driver of sheepdog used hard-coded VDI object size.
> > This patch enables users to handle "block_size_shift" value for
> > calculating VDI object size.
> >
> > When you start qemu, you don't need to specify additional command option.
> >
> > But when you create the VDI which doesn't have default object size
> > with qemu-img command, you specify block_size_shift option.
> >
> > If you want to create a VDI of 8MB(1 << 23) object size,
> > you need to specify following command option.
> >
> >   # qemu-img create -o block_size_shift=23 sheepdog:test1 100M
> >
> > In addition, when you don't specify qemu-img command option,
> > a default value of sheepdog cluster is used for creating VDI.
> >
> >   # qemu-img create sheepdog:test2 100M
> >
> > Signed-off-by: Teruaki Ishizaki <address@hidden>
> > ---
> > V3:
> >   - Delete the needless operation of buffer.
> >   - Delete the needless operations of request header
> >     for SD_OP_GET_CLUSTER_DEFAULT.
> >   - Fix coding style problems.
> >
> > V2:
> >   - Fix coding style problem (white space).
> >   - Add members, store_policy and block_size_shift to struct SheepdogVdiReq
> >   - Initialize request header to use block_size_shift specified by user.
> > ---
> >   block/sheepdog.c          |  140 ++++++++++++++++++++++++++++++++++++++-------
> >   include/block/block_int.h |    1 +
> >   2 files changed, 119 insertions(+), 22 deletions(-)
> >
> > diff --git a/block/sheepdog.c b/block/sheepdog.c
> > index be3176f..c9f06db 100644
> > --- a/block/sheepdog.c
> > +++ b/block/sheepdog.c
> > @@ -37,6 +37,7 @@
> >   #define SD_OP_READ_VDIS      0x15
> >   #define SD_OP_FLUSH_VDI      0x16
> >   #define SD_OP_DEL_VDI        0x17
> > +#define SD_OP_GET_CLUSTER_DEFAULT   0x18
> >
> >   #define SD_FLAG_CMD_WRITE    0x01
> >   #define SD_FLAG_CMD_COW      0x02
> > @@ -167,7 +168,8 @@ typedef struct SheepdogVdiReq {
> >       uint32_t base_vdi_id;
> >       uint8_t copies;
> >       uint8_t copy_policy;
> > -    uint8_t reserved[2];
> > +    uint8_t store_policy;
> > +    uint8_t block_size_shift;
> >       uint32_t snapid;
> >       uint32_t type;
> >       uint32_t pad[2];
> > @@ -186,6 +188,21 @@ typedef struct SheepdogVdiRsp {
> >       uint32_t pad[5];
> >   } SheepdogVdiRsp;
> >
> > +typedef struct SheepdogClusterRsp {
> > +    uint8_t proto_ver;
> > +    uint8_t opcode;
> > +    uint16_t flags;
> > +    uint32_t epoch;
> > +    uint32_t id;
> > +    uint32_t data_length;
> > +    uint32_t result;
> > +    uint8_t nr_copies;
> > +    uint8_t copy_policy;
> > +    uint8_t block_size_shift;
> > +    uint8_t __pad1;
> > +    uint32_t __pad2[6];
> > +} SheepdogClusterRsp;
> > +
> >   typedef struct SheepdogInode {
> >       char name[SD_MAX_VDI_LEN];
> >       char tag[SD_MAX_VDI_TAG_LEN];
> > @@ -1544,6 +1561,7 @@ static int do_sd_create(BDRVSheepdogState *s, uint32_t 
> > *vdi_id, int snapshot,
> >       hdr.vdi_size = s->inode.vdi_size;
> >       hdr.copy_policy = s->inode.copy_policy;
> >       hdr.copies = s->inode.nr_copies;
> > +    hdr.block_size_shift = s->inode.block_size_shift;
> >
> >       ret = do_req(fd, s->aio_context, (SheepdogReq *)&hdr, buf, &wlen, &rlen);
> >
> > @@ -1569,9 +1587,11 @@ static int do_sd_create(BDRVSheepdogState *s, uint32_t 
> > *vdi_id, int snapshot,
> >   static int sd_prealloc(const char *filename, Error **errp)
> >   {
> >       BlockDriverState *bs = NULL;
> > +    BDRVSheepdogState *base = NULL;
> >       uint32_t idx, max_idx;
> > +    uint32_t object_size;
> >       int64_t vdi_size;
> > -    void *buf = g_malloc0(SD_DATA_OBJ_SIZE);
> > +    void *buf = NULL;
> >       int ret;
> >
> >       ret = bdrv_open(&bs, filename, NULL, NULL, BDRV_O_RDWR | BDRV_O_PROTOCOL,
> > @@ -1585,18 +1605,23 @@ static int sd_prealloc(const char *filename, Error 
> > **errp)
> >           ret = vdi_size;
> >           goto out;
> >       }
> > -    max_idx = DIV_ROUND_UP(vdi_size, SD_DATA_OBJ_SIZE);
> > +
> > +    base = bs->opaque;
> > +    object_size = (UINT32_C(1) << base->inode.block_size_shift);
> > +    buf = g_malloc0(object_size);
>
> If I understand correctly, block_size_shift can be up to 31, i.e. this
> is a 2 GB allocation. Do you really think this is a good idea?
I think that it is not best idea.
Sheepdog internal limit of block_size_shift is 31, so I set logical 
limit of block_size_shift for 31.

> At least use g_try_malloc0() here, so that a memory allocation failure
> doesn't crash qemu. (Same goes for all potentially huge allocations that
> you make in the whole codebase.)
As you pointed out, memory allocation was needed for that value.
I suppose that block_size_shift should be up to 26(64MB) or 27(128M)
actually.

Should it be checked actual limits in that source code?

> > +    max_idx = DIV_ROUND_UP(vdi_size, object_size);
> >
> >       for (idx = 0; idx < max_idx; idx++) {
> >           /*
> >            * The created image can be a cloned image, so we need to read
> >            * a data from the source image.
> >            */
> > -        ret = bdrv_pread(bs, idx * SD_DATA_OBJ_SIZE, buf, SD_DATA_OBJ_SIZE);
> > +        ret = bdrv_pread(bs, idx * object_size, buf, object_size);
> >           if (ret < 0) {
> >               goto out;
> >           }
> > -        ret = bdrv_pwrite(bs, idx * SD_DATA_OBJ_SIZE, buf, SD_DATA_OBJ_SIZE);
> > +        ret = bdrv_pwrite(bs, idx * object_size, buf, object_size);
> >           if (ret < 0) {
> >               goto out;
> >           }
> > @@ -1610,7 +1635,9 @@ out_with_err_set:
> >       if (bs) {
> >           bdrv_unref(bs);
> >       }
> > -    g_free(buf);
> > +    if (buf) {
> > +        g_free(buf);
> > +    }
>
> This is unnecessary. g_free(NULL) is valid, it does nothing.
OK, I'll delete those changes.

> >       return ret;
> >   }
> > @@ -1669,6 +1696,17 @@ static int parse_redundancy(BDRVSheepdogState *s, const 
> > char *opt)
> >       return 0;
> >   }
> >
> > +static int parse_block_size_shift(BDRVSheepdogState *s, const char *opt)
> > +{
> > +    struct SheepdogInode *inode = &s->inode;
> > +    inode->block_size_shift = (uint8_t)atoi(opt);
>
> atoi() is best avoided, it has poor error handling.
>
> But I think you don't need this parse function at all, see below.
>
> > +    if (inode->block_size_shift < 20 || inode->block_size_shift > 31) {
> > +        return -EINVAL;
> > +    }
> > +
> > +    return 0;
> > +}
> > +
> >   static int sd_create(const char *filename, QemuOpts *opts,
> >                        Error **errp)
> >   {
> > @@ -1679,6 +1717,7 @@ static int sd_create(const char *filename, QemuOpts *opts,
> >       BDRVSheepdogState *s;
> >       char tag[SD_MAX_VDI_TAG_LEN];
> >       uint32_t snapid;
> > +    uint64_t max_vdi_size;
> >       bool prealloc = false;
> >
> >       s = g_new0(BDRVSheepdogState, 1);
> > @@ -1718,10 +1757,15 @@ static int sd_create(const char *filename, QemuOpts 
> > *opts,
> >           }
> >       }
> >
> > -    if (s->inode.vdi_size > SD_MAX_VDI_SIZE) {
> > -        error_setg(errp, "too big image size");
> > -        ret = -EINVAL;
> > -        goto out;
> > +    g_free(buf);
> > +    buf = qemu_opt_get_del(opts, BLOCK_OPT_BLOCK_SIZE_SHIFT);
> > +    if (buf) {
> > +        ret = parse_block_size_shift(s, buf);
> > +        if (ret < 0) {
> > +            error_setg(errp, "Invalid block_size_shift:"
> > +                             " '%s'. please use 20-31", buf);
> > +            goto out;
> > +        }
> >       }
>
> You could use qemu_opt_get_number_del() here and get a number directly
> from QemuOpts that you don't have to parse any more, if you defined the
> option as QEMU_OPT_NUMBER instead of QEMU_OPT_STRING.
Thank you for your advice!
I'll change to use qemu_opt_get_number_del() and not to use atoi()
function.


> >       if (backing_file) {
> > @@ -1757,6 +1801,45 @@ static int sd_create(const char *filename, QemuOpts 
> > *opts,
> >       }
> >
> >       s->aio_context = qemu_get_aio_context();
> > +
> > +    /* if block_size_shift is not specified, get cluster default value */
> > +    if (s->inode.block_size_shift == 0) {
> > +        SheepdogVdiReq hdr;
> > +        SheepdogClusterRsp *rsp = (SheepdogClusterRsp *)&hdr;
> > +        Error *local_err = NULL;
> > +        int fd;
> > +        unsigned int wlen = 0, rlen = 0;
> > +
> > +        fd = connect_to_sdog(s, &local_err);
> > +        if (fd < 0) {
> > +            error_report("%s", error_get_pretty(local_err));
> > +            error_free(local_err);
> > +            ret = -EIO;
> > +            goto out;
> > +        }
> > +
> > +        memset(&hdr, 0, sizeof(hdr));
> > +        hdr.opcode = SD_OP_GET_CLUSTER_DEFAULT;
> > +        hdr.proto_ver = SD_PROTO_VER;
> > +
> > +        ret = do_req(fd, s->aio_context, (SheepdogReq *)&hdr,
> > +                     NULL, &wlen, &rlen);
> > +        closesocket(fd);
> > +        if (ret) {
> > +            error_setg_errno(errp, -ret, "failed to get cluster default");
> > +            goto out;
> > +        }
> > +        s->inode.block_size_shift = rsp->block_size_shift;
> > +    }
> > +
> > +    max_vdi_size = (UINT64_C(1) << s->inode.block_size_shift) * MAX_DATA_OBJS;
> > +
> > +    if (s->inode.vdi_size > max_vdi_size) {
> > +        error_setg(errp, "too big image size");
>
> Please capitalise the first word in an error messages, i.e. "Too big
> image size".
OK, I'll change an error message properly!

> > +        ret = -EINVAL;
> > +        goto out;
> > +    }
> > +
> >       ret = do_sd_create(s, &vid, 0, errp);
> >       if (ret) {
> >           goto out;

Thanks,
Teruaki Ishizaki