Re: [RFC v3 3/5] file-posix: introduce get_sysfs_long_val for zoned device information.

[Sam Li]

Stefan Hajnoczi <stefanha@redhat.com> 于2022年6月28日周二 16:20写道：
>
> On Mon, Jun 27, 2022 at 08:19:15AM +0800, Sam Li wrote:
> > Use sysfs attribute files to get the zoned device information in case
> > that ioctl() commands of zone management interface won't work. It can
> > return long type of value like chunk_sectors, zoned_append_max_bytes,
> > max_open_zones, max_active_zones.
> > ---
> >  block/file-posix.c | 37 +++++++++++++++++++++++++------------
> >  1 file changed, 25 insertions(+), 12 deletions(-)
> >
> > diff --git a/block/file-posix.c b/block/file-posix.c
> > index 1b8b0d351f..73c2cdfbca 100644
> > --- a/block/file-posix.c
> > +++ b/block/file-posix.c
> > @@ -1216,15 +1216,19 @@ 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 zoned device information (chunk_sectors, zoned_append_max_bytes,
> > + * max_open_zones, max_active_zones) through sysfs attribute files.
>
> This function is also used to get max_segments, which is not related to
> zoned devices. How about:
>
>   Get a block queue sysfs attribute value.
>
> > + */
> > +static long get_sysfs_long_val(int fd, struct stat *st,
> > +                               const char *attribute) {
> >  #ifdef CONFIG_LINUX
> >      char buf[32];
> >      const char *end;
> >      char *sysfspath = NULL;
> >      int ret;
> >      int sysfd = -1;
> > -    long max_segments;
> > +    long val;
> >
> >      if (S_ISCHR(st->st_mode)) {
> >          if (ioctl(fd, SG_GET_SG_TABLESIZE, &ret) == 0) {
> > @@ -1237,8 +1241,9 @@ static int hdev_get_max_segments(int fd, struct stat 
> > *st)
> >          return -ENOTSUP;
> >      }
> >
> > -    sysfspath = g_strdup_printf("/sys/dev/block/%u:%u/queue/max_segments",
> > -                                major(st->st_rdev), minor(st->st_rdev));
> > +    sysfspath = g_strdup_printf("/sys/dev/block/%u:%u/queue/%s",
> > +                                major(st->st_rdev), minor(st->st_rdev),
> > +                                attribute);
> >      sysfd = open(sysfspath, O_RDONLY);
> >      if (sysfd == -1) {
> >          ret = -errno;
> > @@ -1256,9 +1261,9 @@ static int hdev_get_max_segments(int fd, struct stat 
> > *st)
> >      }
> >      buf[ret] = 0;
> >      /* The file is ended with '\n', pass 'end' to accept that. */
> > -    ret = qemu_strtol(buf, &end, 10, &max_segments);
> > +    ret = qemu_strtol(buf, &end, 10, &val);
> >      if (ret == 0 && end && *end == '\n') {
> > -        ret = max_segments;
> > +        ret = val;
> >      }
> >
> >  out:
> > @@ -1272,6 +1277,15 @@ out:
> >  #endif
> >  }
> >
> > +static int hdev_get_max_segments(int fd, struct stat *st) {
> > +    int ret;
> > +    ret = get_sysfs_long_val(fd, st, "max_segments");
> > +    if (ret < 0) {
> > +        return -1;
>
> This hides the actual error number. The if statement can be dropped and
> the function can be simplified to:
>
>   static int hdev_get_max_segments(int fd, struct stat *st) {
>       return get_sysfs_long_val(fd, st, "max_segments");
>   }
>
> Whether you want to keep the tiny helper function or inline
> get_sysfs_long_val(fd, st, "max_segments") into the caller is up to you.
>
> > +    }
> > +    return ret;
> > +}
> > +
> >  static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
> >  {
> >      BDRVRawState *s = bs->opaque;
> > @@ -1872,6 +1886,7 @@ static int handle_aiocb_zone_report(void *opaque) {
> >
> >  static int handle_aiocb_zone_mgmt(void *opaque) {
> >      RawPosixAIOData *aiocb = opaque;
> > +    BlockDriverState *s = aiocb->bs;
> >      int fd = aiocb->aio_fildes;
> >      int64_t offset = aiocb->aio_offset;
> >      int64_t len = aiocb->aio_nbytes;
> > @@ -1884,11 +1899,9 @@ static int handle_aiocb_zone_mgmt(void *opaque) {
> >      int64_t zone_size_mask;
> >      int ret;
> >
> > -    ret = ioctl(fd, BLKGETZONESZ, &zone_size);
> > -    if (ret) {
> > -        return -1;
> > -    }
> > -
> > +    g_autofree struct stat *file = g_new(struct stat, 1);
> > +    stat(s->filename, file);
>
> There is no need to allocate struct stat using g_new(). It's a small
> struct that can be on the stack.
>
> Also, fstat(fd, &st) is preferred when the file descriptor is already
> open because it avoids race conditions due to file renaming/path
> traversal.
>
> Here is how this could be written:
>
>   struct stat st;
>   if (fstat(fd, &st) < 0) {
>       return -errno;
>   }

Thanks for the suggestions!

>
> > +    zone_size = get_sysfs_long_val(fd, file, "chunk_sectors");
> >      zone_size_mask = zone_size - 1;
> >      if (offset & zone_size_mask) {
> >          error_report("offset is not the start of a zone");
> > --
> > 2.35.3
> >