Re: [PATCH v4 4/7] file-posix: try BLKSECTGET on block devices too, do not round to power of 2

2021-06-09 Thread Maxim Levitsky 
On Tue, 2021-06-08 at 15:16 +0200, Paolo Bonzini wrote:
> bs->sg is only true for character devices, but block devices can also
> be used with scsi-block and scsi-generic.  Unfortunately BLKSECTGET
> returns bytes in an int for /dev/sgN devices, and sectors in a short
> for block devices, so account for that in the code.
> 
> The maximum transfer also need not be a power of 2 (for example I have
> seen disks with 1280 KiB maximum transfer) so there's no need to pass
> the result through pow2floor.
> 
> Signed-off-by: Paolo Bonzini 
> ---
>  block/file-posix.c | 44 
>  1 file changed, 24 insertions(+), 20 deletions(-)
> 
> diff --git a/block/file-posix.c b/block/file-posix.c
> index c9746d3eb6..1439293f63 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -1149,22 +1149,27 @@ static void raw_reopen_abort(BDRVReopenState *state)
>  s->reopen_state = NULL;
>  }
>  
> -static int sg_get_max_transfer_length(int fd)
> +static int hdev_get_max_hw_transfer(int fd, struct stat *st)
>  {
>  #ifdef BLKSECTGET
> -int max_bytes = 0;
> -
> -if (ioctl(fd, BLKSECTGET, _bytes) == 0) {
> -return max_bytes;
> +if (S_ISBLK(st->st_mode)) {
> +unsigned short max_sectors = 0;
> +if (ioctl(fd, BLKSECTGET, _sectors) == 0) {
> +return max_sectors * 512;
> +}
>  } else {
> -return -errno;
> +int max_bytes = 0;
> +if (ioctl(fd, BLKSECTGET, _bytes) == 0) {

Again I would use the bs->sg for that.

> +return max_bytes;
> +}
>  }
> +return -errno;
>  #else
>  return -ENOSYS;
>  #endif
>  }
>  
> -static int sg_get_max_segments(int fd)
> +static int hdev_get_max_segments(int fd, struct stat *st)
>  {
>  #ifdef CONFIG_LINUX
>  char buf[32];
> @@ -1173,26 +1178,20 @@ static int sg_get_max_segments(int fd)
>  int ret;
>  int sysfd = -1;
>  long max_segments;
> -struct stat st;
>  
> -if (fstat(fd, )) {
> -ret = -errno;
> -goto out;
> -}
> -
> -if (S_ISCHR(st.st_mode)) {
> +if (S_ISCHR(st->st_mode)) {
>  if (ioctl(fd, SG_GET_SG_TABLESIZE, ) == 0) {
>  return ret;
>  }
>  return -ENOTSUP;
>  }
>  
> -if (!S_ISBLK(st.st_mode)) {
> +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));
> +major(st->st_rdev), minor(st->st_rdev));
>  sysfd = open(sysfspath, O_RDONLY);
>  if (sysfd == -1) {
>  ret = -errno;
> @@ -1229,15 +1228,20 @@ out:
>  static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
>  {
>  BDRVRawState *s = bs->opaque;
> +struct stat st;
> +
> +if (fstat(s->fd, )) {
> +return;
> +}
>  
> -if (bs->sg) {
> -int ret = sg_get_max_transfer_length(s->fd);
> +if (bs->sg || S_ISBLK(st.st_mode)) {
> +int ret = hdev_get_max_hw_transfer(s->fd, );
>  
>  if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) {
> -bs->bl.max_hw_transfer = pow2floor(ret);
> +bs->bl.max_hw_transfer = ret;
>  }
>  
> -ret = sg_get_max_segments(s->fd);
> +ret = hdev_get_max_segments(s->fd, );
>  if (ret > 0) {
>  bs->bl.max_iov = ret;
>  }


Roughly speaking this looks correct, but I might have missed something as well.

This is roughly the same as patches from Tom Yan which I carried in my series

https://www.mail-archive.com/qemu-devel@nongnu.org/msg768258.html
https://www.mail-archive.com/qemu-devel@nongnu.org/msg768262.html


I like a bit more how he created separate functions for /dev/sg and for all 
other block devices.
Please take a look.

Also not related to this patch, you are missing my fix I did to the VPD limit 
emulation, please consider taking
it into the series:

https://www.mail-archive.com/qemu-devel@nongnu.org/msg768260.html


Best regards,
Maxim Levitsky

Re: [PATCH v4 4/7] file-posix: try BLKSECTGET on block devices too, do not round to power of 2

2021-06-08 Thread Eric Blake 
On Tue, Jun 08, 2021 at 03:16:31PM +0200, Paolo Bonzini wrote:
> bs->sg is only true for character devices, but block devices can also
> be used with scsi-block and scsi-generic.  Unfortunately BLKSECTGET
> returns bytes in an int for /dev/sgN devices, and sectors in a short
> for block devices, so account for that in the code.

Gotta love inconsistent and poorly-documented kernel interfaces! (on my
system, 'man -k BLKSECTGET' had no hits)

> 
> The maximum transfer also need not be a power of 2 (for example I have
> seen disks with 1280 KiB maximum transfer) so there's no need to pass
> the result through pow2floor.
> 
> Signed-off-by: Paolo Bonzini 
> ---
>  block/file-posix.c | 44 
>  1 file changed, 24 insertions(+), 20 deletions(-)
>

Reviewed-by: Eric Blake 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.   +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

[PATCH v4 4/7] file-posix: try BLKSECTGET on block devices too, do not round to power of 2

2021-06-08 Thread Paolo Bonzini 
bs->sg is only true for character devices, but block devices can also
be used with scsi-block and scsi-generic.  Unfortunately BLKSECTGET
returns bytes in an int for /dev/sgN devices, and sectors in a short
for block devices, so account for that in the code.

The maximum transfer also need not be a power of 2 (for example I have
seen disks with 1280 KiB maximum transfer) so there's no need to pass
the result through pow2floor.

Signed-off-by: Paolo Bonzini 
---
 block/file-posix.c | 44 
 1 file changed, 24 insertions(+), 20 deletions(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index c9746d3eb6..1439293f63 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1149,22 +1149,27 @@ static void raw_reopen_abort(BDRVReopenState *state)
 s->reopen_state = NULL;
 }
 
-static int sg_get_max_transfer_length(int fd)
+static int hdev_get_max_hw_transfer(int fd, struct stat *st)
 {
 #ifdef BLKSECTGET
-int max_bytes = 0;
-
-if (ioctl(fd, BLKSECTGET, _bytes) == 0) {
-return max_bytes;
+if (S_ISBLK(st->st_mode)) {
+unsigned short max_sectors = 0;
+if (ioctl(fd, BLKSECTGET, _sectors) == 0) {
+return max_sectors * 512;
+}
 } else {
-return -errno;
+int max_bytes = 0;
+if (ioctl(fd, BLKSECTGET, _bytes) == 0) {
+return max_bytes;
+}
 }
+return -errno;
 #else
 return -ENOSYS;
 #endif
 }
 
-static int sg_get_max_segments(int fd)
+static int hdev_get_max_segments(int fd, struct stat *st)
 {
 #ifdef CONFIG_LINUX
 char buf[32];
@@ -1173,26 +1178,20 @@ static int sg_get_max_segments(int fd)
 int ret;
 int sysfd = -1;
 long max_segments;
-struct stat st;
 
-if (fstat(fd, )) {
-ret = -errno;
-goto out;
-}
-
-if (S_ISCHR(st.st_mode)) {
+if (S_ISCHR(st->st_mode)) {
 if (ioctl(fd, SG_GET_SG_TABLESIZE, ) == 0) {
 return ret;
 }
 return -ENOTSUP;
 }
 
-if (!S_ISBLK(st.st_mode)) {
+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));
+major(st->st_rdev), minor(st->st_rdev));
 sysfd = open(sysfspath, O_RDONLY);
 if (sysfd == -1) {
 ret = -errno;
@@ -1229,15 +1228,20 @@ out:
 static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
 {
 BDRVRawState *s = bs->opaque;
+struct stat st;
+
+if (fstat(s->fd, )) {
+return;
+}
 
-if (bs->sg) {
-int ret = sg_get_max_transfer_length(s->fd);
+if (bs->sg || S_ISBLK(st.st_mode)) {
+int ret = hdev_get_max_hw_transfer(s->fd, );
 
 if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) {
-bs->bl.max_hw_transfer = pow2floor(ret);
+bs->bl.max_hw_transfer = ret;
 }
 
-ret = sg_get_max_segments(s->fd);
+ret = hdev_get_max_segments(s->fd, );
 if (ret > 0) {
 bs->bl.max_iov = ret;
 }
-- 
2.31.1