Re: [PULL v2 02/16] block/file-posix: introduce helper functions for sysfs attributes

[Sam Li]

Matthew Rosato <mjrosato@linux.ibm.com> 于2023年6月1日周四 02:21写道：
>
> On 5/15/23 12:04 PM, Stefan Hajnoczi wrote:
> > From: Sam Li <faithilikerun@gmail.com>
> >
> > Use get_sysfs_str_val() to get the string value of device
> > zoned model. Then get_sysfs_zoned_model() can convert it to
> > BlockZoneModel type of QEMU.
> >
> > Use get_sysfs_long_val() to get the long value of zoned device
> > information.
>
> Hi Stefan, Sam,
>
> I am having an issue on s390x using virtio-blk-{pci,ccw} backed by an NVMe 
> partition, and I've bisected the root cause to this commit.
>
> I noticed that tests which use the partition e.g. /dev/nvme0n1p1 as a backing 
> device would fail, but those that use the namespace e.g. /dev/nvme0n1 would 
> still succeed.  The root issue appears to be that the block device associated 
> with the partition does not have a "max_segments" attribute, and prior to 
> this patch hdev_get_max_segment() would return -ENOENT in this case.  After 
> this patch, however, QEMU is instead crashing.  It looks like 
> g_file_get_contents is returning 0 with a len == 0 if the specified sysfs 
> path does not exist.  The following diff on top seems to resolve the issue 
> for me:
>
>
> diff --git a/block/file-posix.c b/block/file-posix.c
> index 0ab158efba2..eeb0247c74e 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -1243,7 +1243,7 @@ static int get_sysfs_str_val(struct stat *st, const 
> char *attribute,
>                                  major(st->st_rdev), minor(st->st_rdev),
>                                  attribute);
>      ret = g_file_get_contents(sysfspath, val, &len, NULL);
> -    if (ret == -1) {
> +    if (ret == -1 || len == 0) {
>          return -ENOENT;
>      }
>

Hi Matthew,

Thanks for the information. After some checking, I think the bug here
is that g_file_get_contens returns g_boolean value and the error case
will return 0 instead of -1 in my previous code. Can the following
line fix your issue on the s390x device?

+ if (ret == FALSE) {

https://docs.gtk.org/glib/func.file_get_contents.html

Thanks,
Sam




>
>
>
> >
> > Signed-off-by: Sam Li <faithilikerun@gmail.com>
> > Reviewed-by: Hannes Reinecke <hare@suse.de>
> > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
> > Reviewed-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
> > Acked-by: Kevin Wolf <kwolf@redhat.com>
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > Message-id: 20230508045533.175575-3-faithilikerun@gmail.com
> > Message-id: 20230324090605.28361-3-faithilikerun@gmail.com
> > [Adjust commit message prefix as suggested by Philippe Mathieu-Daudé
> > <philmd@linaro.org>.
> > --Stefan]
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > ---
> >  include/block/block_int-common.h |   3 +
> >  block/file-posix.c               | 135 ++++++++++++++++++++++---------
> >  2 files changed, 100 insertions(+), 38 deletions(-)
> >
> > diff --git a/include/block/block_int-common.h 
> > b/include/block/block_int-common.h
> > index 4909876756..c7ca5a83e9 100644
> > --- a/include/block/block_int-common.h
> > +++ b/include/block/block_int-common.h
> > @@ -862,6 +862,9 @@ typedef struct BlockLimits {
> >       * an explicit monitor command to load the disk inside the guest).
> >       */
> >      bool has_variable_length;
> > +
> > +    /* device zone model */
> > +    BlockZoneModel zoned;
> >  } BlockLimits;
> >
> >  typedef struct BdrvOpBlocker BdrvOpBlocker;
> > diff --git a/block/file-posix.c b/block/file-posix.c
> > index c7b723368e..97c597a2a0 100644
> > --- a/block/file-posix.c
> > +++ b/block/file-posix.c
> > @@ -1202,15 +1202,89 @@ static int hdev_get_max_hw_transfer(int fd, struct 
> > stat *st)
> >  #endif
> >  }
> >
> > -static int hdev_get_max_segments(int fd, struct stat *st)
> > +/*
> > + * Get a sysfs attribute value as character string.
> > + */
> > +#ifdef CONFIG_LINUX
> > +static int get_sysfs_str_val(struct stat *st, const char *attribute,
> > +                             char **val) {
> > +    g_autofree char *sysfspath = NULL;
> > +    int ret;
> > +    size_t len;
> > +
> > +    if (!S_ISBLK(st->st_mode)) {
> > +        return -ENOTSUP;
> > +    }
> > +
> > +    sysfspath = g_strdup_printf("/sys/dev/block/%u:%u/queue/%s",
> > +                                major(st->st_rdev), minor(st->st_rdev),
> > +                                attribute);
> > +    ret = g_file_get_contents(sysfspath, val, &len, NULL);
> > +    if (ret == -1) {
> > +        return -ENOENT;
> > +    }
> > +
> > +    /* The file is ended with '\n' */
> > +    char *p;
> > +    p = *val;
> > +    if (*(p + len - 1) == '\n') {
> > +        *(p + len - 1) = '\0';
> > +    }
> > +    return ret;
> > +}
> > +#endif
> > +
> > +static int get_sysfs_zoned_model(struct stat *st, BlockZoneModel *zoned)
> >  {
> > +    g_autofree char *val = NULL;
> > +    int ret;
> > +
> > +    ret = get_sysfs_str_val(st, "zoned", &val);
> > +    if (ret < 0) {
> > +        return ret;
> > +    }
> > +
> > +    if (strcmp(val, "host-managed") == 0) {
> > +        *zoned = BLK_Z_HM;
> > +    } else if (strcmp(val, "host-aware") == 0) {
> > +        *zoned = BLK_Z_HA;
> > +    } else if (strcmp(val, "none") == 0) {
> > +        *zoned = BLK_Z_NONE;
> > +    } else {
> > +        return -ENOTSUP;
> > +    }
> > +    return 0;
> > +}
> > +
> > +/*
> > + * Get a sysfs attribute value as a long integer.
> > + */
> >  #ifdef CONFIG_LINUX
> > -    char buf[32];
> > +static long get_sysfs_long_val(struct stat *st, const char *attribute)
> > +{
> > +    g_autofree char *str = NULL;
> >      const char *end;
> > -    char *sysfspath = NULL;
> > +    long val;
> > +    int ret;
> > +
> > +    ret = get_sysfs_str_val(st, attribute, &str);
> > +    if (ret < 0) {
> > +        return ret;
> > +    }
> > +
> > +    /* The file is ended with '\n', pass 'end' to accept that. */
> > +    ret = qemu_strtol(str, &end, 10, &val);
> > +    if (ret == 0 && end && *end == '\0') {
> > +        ret = val;
> > +    }
> > +    return ret;
> > +}
> > +#endif
> > +
> > +static int hdev_get_max_segments(int fd, struct stat *st)
> > +{
> > +#ifdef CONFIG_LINUX
> >      int ret;
> > -    int sysfd = -1;
> > -    long max_segments;
> >
> >      if (S_ISCHR(st->st_mode)) {
> >          if (ioctl(fd, SG_GET_SG_TABLESIZE, &ret) == 0) {
> > @@ -1218,44 +1292,27 @@ static int hdev_get_max_segments(int fd, struct 
> > stat *st)
> >          }
> >          return -ENOTSUP;
> >      }
> > -
> > -    if (!S_ISBLK(st->st_mode)) {
> > -        return -ENOTSUP;
> > -    }
> > -
> > -    sysfspath = g_strdup_printf("/sys/dev/block/%u:%u/queue/max_segments",
> > -                                major(st->st_rdev), minor(st->st_rdev));
> > -    sysfd = open(sysfspath, O_RDONLY);
> > -    if (sysfd == -1) {
> > -        ret = -errno;
> > -        goto out;
> > -    }
> > -    ret = RETRY_ON_EINTR(read(sysfd, buf, sizeof(buf) - 1));
> > -    if (ret < 0) {
> > -        ret = -errno;
> > -        goto out;
> > -    } else if (ret == 0) {
> > -        ret = -EIO;
> > -        goto out;
> > -    }
> > -    buf[ret] = 0;
> > -    /* The file is ended with '\n', pass 'end' to accept that. */
> > -    ret = qemu_strtol(buf, &end, 10, &max_segments);
> > -    if (ret == 0 && end && *end == '\n') {
> > -        ret = max_segments;
> > -    }
> > -
> > -out:
> > -    if (sysfd != -1) {
> > -        close(sysfd);
> > -    }
> > -    g_free(sysfspath);
> > -    return ret;
> > +    return get_sysfs_long_val(st, "max_segments");
> >  #else
> >      return -ENOTSUP;
> >  #endif
> >  }
> >
> > +static void raw_refresh_zoned_limits(BlockDriverState *bs, struct stat *st,
> > +                                     Error **errp)
> > +{
> > +    BlockZoneModel zoned;
> > +    int ret;
> > +
> > +    bs->bl.zoned = BLK_Z_NONE;
> > +
> > +    ret = get_sysfs_zoned_model(st, &zoned);
> > +    if (ret < 0 || zoned == BLK_Z_NONE) {
> > +        return;
> > +    }
> > +    bs->bl.zoned = zoned;
> > +}
> > +
> >  static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
> >  {
> >      BDRVRawState *s = bs->opaque;
> > @@ -1297,6 +1354,8 @@ static void raw_refresh_limits(BlockDriverState *bs, 
> > Error **errp)
> >              bs->bl.max_hw_iov = ret;
> >          }
> >      }
> > +
> > +    raw_refresh_zoned_limits(bs, &st, errp);
> >  }
> >
> >  static int check_for_dasd(int fd)
>