[Qemu-devel] [PATCH v3 0/5] Some fixes related to scsi-generic

[Qemu-devel] [PATCH v3 0/5] Some fixes related to scsi-generic

[Dimitris Aragiorgis]

Hi all,

These four patches make slight changes to the way QEMU handles SCSI
generic devices to fix a number of small problems.

I am sending them against the master branch, since I don't know if they
can be considered bugfixes.

Thanks,
dimara

v3 (rebased to current master):
* Avoid bit-rot in DPRINTF (adopt Eric's suggestion)
* Address Kevin's comments (DEBUF_FLOPPY, line > 80 chars, SG device)
* Mention Kevin's comment wrt disk flush in the corresponding commit

v2:
* remove duplicate check for sg inside iscsi_co_flush()
* remove DEBUG_BLOCK_PRINT in block/raw-posix.c
* use DPRINTF for debugging in block/raw-posix.c

PS: Paolo suggested to use a tracepoint inside hdev_is_sg() but I chose DPRINTF
instead. It would make sense to add a tracepoint for bdrv_is_sg() (just like
most bdrv_* commands) but this is too much for now since it just returns the
bs->sg flag (and is not an actual driver function). If you insist I'll change
it in v3.

Dimitris Aragiorgis (5):
  block: Use bdrv_is_sg() everywhere
  Fix migration in case of scsi-generic
  raw-posix: DPRINTF instead of DEBUG_BLOCK_PRINT
  raw-posix: Use DPRINTF for DEBUG_FLOPPY
  raw-posix: Introduce hdev_is_sg()

 block.c           |    6 ++--
 block/io.c        |    3 +-
 block/iscsi.c     |    4 ---
 block/raw-posix.c |   82 ++++++++++++++++++++++++++++++-----------------------
 4 files changed, 51 insertions(+), 44 deletions(-)

-- 
1.7.10.4

[Qemu-devel] [PATCH v3 1/5] block: Use bdrv_is_sg() everywhere

[Dimitris Aragiorgis]

Instead of checking bs->sg use bdrv_is_sg() consistently throughout
the code.

Signed-off-by: Dimitris Aragiorgis <dimara@arrikto.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
---
 block.c           |    6 +++---
 block/iscsi.c     |    2 +-
 block/raw-posix.c |    4 ++--
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/block.c b/block.c
index 7904098..d651b57 100644
--- a/block.c
+++ b/block.c
@@ -566,7 +566,7 @@ static int find_image_format(BlockDriverState *bs, const char *filename,
     int ret = 0;
 
     /* Return the raw BlockDriver * to scsi-generic devices or empty drives */
-    if (bs->sg || !bdrv_is_inserted(bs) || bdrv_getlength(bs) == 0) {
+    if (bdrv_is_sg(bs) || !bdrv_is_inserted(bs) || bdrv_getlength(bs) == 0) {
         *pdrv = &bdrv_raw;
         return ret;
     }
@@ -598,7 +598,7 @@ static int refresh_total_sectors(BlockDriverState *bs, int64_t hint)
     BlockDriver *drv = bs->drv;
 
     /* Do not attempt drv->bdrv_getlength() on scsi-generic devices */
-    if (bs->sg)
+    if (bdrv_is_sg(bs))
         return 0;
 
     /* query actual device if possible, otherwise just trust the hint */
@@ -890,7 +890,7 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
     }
 
     assert(bdrv_opt_mem_align(bs) != 0);
-    assert((bs->request_alignment != 0) || bs->sg);
+    assert((bs->request_alignment != 0) || bdrv_is_sg(bs));
     return 0;
 
 free_and_fail:
diff --git a/block/iscsi.c b/block/iscsi.c
index 8fca1d3..502a81f 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -627,7 +627,7 @@ static int coroutine_fn iscsi_co_flush(BlockDriverState *bs)
     IscsiLun *iscsilun = bs->opaque;
     struct IscsiTask iTask;
 
-    if (bs->sg) {
+    if (bdrv_is_sg(bs)) {
         return 0;
     }
 
diff --git a/block/raw-posix.c b/block/raw-posix.c
index 24d8582..fb58440 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -302,9 +302,9 @@ static void raw_probe_alignment(BlockDriverState *bs, int fd, Error **errp)
     BDRVRawState *s = bs->opaque;
     char *buf;
 
-    /* For /dev/sg devices the alignment is not really used.
+    /* For SCSI generic devices the alignment is not really used.
        With buffered I/O, we don't have any restrictions. */
-    if (bs->sg || !s->needs_alignment) {
+    if (bdrv_is_sg(bs) || !s->needs_alignment) {
         bs->request_alignment = 1;
         s->buf_align = 1;
         return;
-- 
1.7.10.4

[Qemu-devel] [PATCH v3 2/5] Fix migration in case of scsi-generic

[Dimitris Aragiorgis]

During migration, QEMU uses fsync()/fdatasync() on the open file
descriptor for read-write block devices to flush data just before
stopping the VM.

However, fsync() on a scsi-generic device returns -EINVAL which
causes the migration to fail. This patch skips flushing data in case
of an SG device, since submitting SCSI commands directly via an SG
character device (e.g. /dev/sg0) bypasses the page cache completely,
anyway.

Note that fsync() not only flushes the page cache but also the disk
cache. The scsi-generic device never sends flushes, and for
migration it assumes that the same SCSI device is used by the
destination host, so it does not issue any SCSI SYNCHRONIZE CACHE
(10) command.

Finally, remove the bdrv_is_sg() test from iscsi_co_flush() since
this is now redundant (we flush the underlying protocol at the end
of bdrv_co_flush() which, with this patch, we never reach).

Signed-off-by: Dimitris Aragiorgis <dimara@arrikto.com>
---
 block/io.c    |    3 ++-
 block/iscsi.c |    4 ----
 2 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/block/io.c b/block/io.c
index 1ce62c4..922dc07 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2231,7 +2231,8 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
 {
     int ret;
 
-    if (!bs || !bdrv_is_inserted(bs) || bdrv_is_read_only(bs)) {
+    if (!bs || !bdrv_is_inserted(bs) || bdrv_is_read_only(bs) ||
+        bdrv_is_sg(bs)) {
         return 0;
     }
 
diff --git a/block/iscsi.c b/block/iscsi.c
index 502a81f..965978b 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -627,10 +627,6 @@ static int coroutine_fn iscsi_co_flush(BlockDriverState *bs)
     IscsiLun *iscsilun = bs->opaque;
     struct IscsiTask iTask;
 
-    if (bdrv_is_sg(bs)) {
-        return 0;
-    }
-
     if (!iscsilun->force_next_flush) {
         return 0;
     }
-- 
1.7.10.4

[Qemu-devel] [PATCH v3 3/5] raw-posix: DPRINTF instead of DEBUG_BLOCK_PRINT

[Dimitris Aragiorgis]

Building the QEMU tools fails if we #define DEBUG_BLOCK inside
block/raw-posix.c. Here instead of adding qemu-log.o in block-obj-y
so that DEBUG_BLOCK_PRINT can be used, we substitute the latter with
a simple DPRINTF() (that does not cause bit-rot).

Signed-off-by: Dimitris Aragiorgis <dimara@arrikto.com>
---
 block/raw-posix.c |   17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/block/raw-posix.c b/block/raw-posix.c
index fb58440..ff7dc4d 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -97,12 +97,17 @@
 //#define DEBUG_FLOPPY
 
 //#define DEBUG_BLOCK
-#if defined(DEBUG_BLOCK)
-#define DEBUG_BLOCK_PRINT(formatCstr, ...) do { if (qemu_log_enabled()) \
-    { qemu_log(formatCstr, ## __VA_ARGS__); qemu_log_flush(); } } while (0)
+
+#ifdef DEBUG_BLOCK
+# define DEBUG_BLOCK_PRINT 1
 #else
-#define DEBUG_BLOCK_PRINT(formatCstr, ...)
+# define DEBUG_BLOCK_PRINT 0
 #endif
+#define DPRINTF(fmt, ...) \
+do { \
+    if (DEBUG_BLOCK_PRINT) \
+        printf(fmt, ## __VA_ARGS__); \
+} while (0)
 
 /* OS X does not have O_DSYNC */
 #ifndef O_DSYNC
@@ -1023,7 +1028,7 @@ static int xfs_write_zeroes(BDRVRawState *s, int64_t offset, uint64_t bytes)
     fl.l_len = bytes;
 
     if (xfsctl(NULL, s->fd, XFS_IOC_ZERO_RANGE, &fl) < 0) {
-        DEBUG_BLOCK_PRINT("cannot write zero range (%s)\n", strerror(errno));
+        DPRINTF("cannot write zero range (%s)\n", strerror(errno));
         return -errno;
     }
 
@@ -1040,7 +1045,7 @@ static int xfs_discard(BDRVRawState *s, int64_t offset, uint64_t bytes)
     fl.l_len = bytes;
 
     if (xfsctl(NULL, s->fd, XFS_IOC_UNRESVSP64, &fl) < 0) {
-        DEBUG_BLOCK_PRINT("cannot punch hole (%s)\n", strerror(errno));
+        DPRINTF("cannot punch hole (%s)\n", strerror(errno));
         return -errno;
     }
 
-- 
1.7.10.4

Re: [Qemu-devel] [PATCH v3 3/5] raw-posix: DPRINTF instead of DEBUG_BLOCK_PRINT

[Eric Blake]

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On 05/14/2015 05:01 AM, Dimitris Aragiorgis wrote:
> Building the QEMU tools fails if we #define DEBUG_BLOCK inside
> block/raw-posix.c. Here instead of adding qemu-log.o in block-obj-y
> so that DEBUG_BLOCK_PRINT can be used, we substitute the latter with
> a simple DPRINTF() (that does not cause bit-rot).
> 
> Signed-off-by: Dimitris Aragiorgis <dimara@arrikto.com>
> ---
>  block/raw-posix.c |   17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 

> +#define DPRINTF(fmt, ...) \
> +do { \
> +    if (DEBUG_BLOCK_PRINT) \
> +        printf(fmt, ## __VA_ARGS__); \
> +} while (0)

Still missing {} for the if statement.

[It might be nice to update scripts/checkpatch.pl to catch correct {}
inside macros, but that's a project for a different day.]

> @@ -1023,7 +1028,7 @@ static int xfs_write_zeroes(BDRVRawState *s, int64_t offset, uint64_t bytes)
>      fl.l_len = bytes;
>  
>      if (xfsctl(NULL, s->fd, XFS_IOC_ZERO_RANGE, &fl) < 0) {
> -        DEBUG_BLOCK_PRINT("cannot write zero range (%s)\n", strerror(errno));
> +        DPRINTF("cannot write zero range (%s)\n", strerror(errno));
>          return -errno;
>      }

Pre-existing bug - strerror() and/or DPRINTF() can clobber errno, so
your return value may be destroyed.  You'll have to save errno into a
temporary variable prior to DPRINTF, and return that value.

>  
> @@ -1040,7 +1045,7 @@ static int xfs_discard(BDRVRawState *s, int64_t offset, uint64_t bytes)
>      fl.l_len = bytes;
>  
>      if (xfsctl(NULL, s->fd, XFS_IOC_UNRESVSP64, &fl) < 0) {
> -        DEBUG_BLOCK_PRINT("cannot punch hole (%s)\n", strerror(errno));
> +        DPRINTF("cannot punch hole (%s)\n", strerror(errno));
>          return -errno;

Here too.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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[Qemu-devel] [PATCH v3 4/5] raw-posix: Use DPRINTF for DEBUG_FLOPPY

[Dimitris Aragiorgis]

Get rid of several #ifdef DEBUG_FLOPPY and substitute them with
DPRINTF.

Signed-off-by: Dimitris Aragiorgis <dimara@arrikto.com>
---
 block/raw-posix.c |   22 +++++-----------------
 1 file changed, 5 insertions(+), 17 deletions(-)

diff --git a/block/raw-posix.c b/block/raw-posix.c
index ff7dc4d..82e522f 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -94,8 +94,6 @@
 #include <xfs/xfs.h>
 #endif
 
-//#define DEBUG_FLOPPY
-
 //#define DEBUG_BLOCK
 
 #ifdef DEBUG_BLOCK
@@ -2162,16 +2160,12 @@ static int fd_open(BlockDriverState *bs)
         (qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - s->fd_open_time) >= FD_OPEN_TIMEOUT) {
         qemu_close(s->fd);
         s->fd = -1;
-#ifdef DEBUG_FLOPPY
-        printf("Floppy closed\n");
-#endif
+        DPRINTF("Floppy closed\n");
     }
     if (s->fd < 0) {
         if (s->fd_got_error &&
             (qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - s->fd_error_time) < FD_OPEN_TIMEOUT) {
-#ifdef DEBUG_FLOPPY
-            printf("No floppy (open delayed)\n");
-#endif
+            DPRINTF("No floppy (open delayed)\n");
             return -EIO;
         }
         s->fd = qemu_open(bs->filename, s->open_flags & ~O_NONBLOCK);
@@ -2180,14 +2174,10 @@ static int fd_open(BlockDriverState *bs)
             s->fd_got_error = 1;
             if (last_media_present)
                 s->fd_media_changed = 1;
-#ifdef DEBUG_FLOPPY
-            printf("No floppy\n");
-#endif
+            DPRINTF("No floppy\n");
             return -EIO;
         }
-#ifdef DEBUG_FLOPPY
-        printf("Floppy opened\n");
-#endif
+        DPRINTF("Floppy opened\n");
     }
     if (!last_media_present)
         s->fd_media_changed = 1;
@@ -2455,9 +2445,7 @@ static int floppy_media_changed(BlockDriverState *bs)
     fd_open(bs);
     ret = s->fd_media_changed;
     s->fd_media_changed = 0;
-#ifdef DEBUG_FLOPPY
-    printf("Floppy changed=%d\n", ret);
-#endif
+    DPRINTF("Floppy changed=%d\n", ret);
     return ret;
 }
 
-- 
1.7.10.4

[Qemu-devel] [PATCH v3 5/5] raw-posix: Introduce hdev_is_sg()

[Dimitris Aragiorgis]

Until now, an SG device was identified only by checking if its path
started with "/dev/sg". Then, hdev_open() set bs->sg accordingly.
This is very fragile, e.g. it fails with symlinks or relative paths.
We should rely on the actual properties of the device instead of the
specified file path.

Test for an SG device (e.g. /dev/sg0) by ensuring that all of the
following holds:

 - The device supports the SG_GET_VERSION_NUM ioctl
 - The device supports the SG_GET_SCSI_ID ioctl
 - The specified file name corresponds to a character device

Signed-off-by: Dimitris Aragiorgis <dimara@arrikto.com>
---
 block/raw-posix.c |   39 ++++++++++++++++++++++++++++-----------
 1 file changed, 28 insertions(+), 11 deletions(-)

diff --git a/block/raw-posix.c b/block/raw-posix.c
index 82e522f..19b90d1 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -57,6 +57,7 @@
 #include <linux/fd.h>
 #include <linux/fs.h>
 #include <linux/hdreg.h>
+#include <scsi/sg.h>
 #ifdef __s390__
 #include <asm/dasd.h>
 #endif
@@ -2076,15 +2077,38 @@ static void hdev_parse_filename(const char *filename, QDict *options,
     qdict_put_obj(options, "filename", QOBJECT(qstring_from_str(filename)));
 }
 
+static int hdev_is_sg(BlockDriverState *bs)
+{
+
+#if defined(__linux__)
+
+    struct stat st;
+    struct sg_scsi_id scsiid;
+    int sg_version;
+
+    if (!bdrv_ioctl(bs, SG_GET_VERSION_NUM, &sg_version) &&
+        !bdrv_ioctl(bs, SG_GET_SCSI_ID, &scsiid) &&
+        stat(bs->filename, &st) >= 0 && S_ISCHR(st.st_mode)) {
+        DPRINTF("SG device found: type=%d, version=%d\n",
+            scsiid.scsi_type, sg_version);
+        return 1;
+    }
+
+#endif
+
+    return 0;
+}
+
 static int hdev_open(BlockDriverState *bs, QDict *options, int flags,
                      Error **errp)
 {
     BDRVRawState *s = bs->opaque;
     Error *local_err = NULL;
     int ret;
-    const char *filename = qdict_get_str(options, "filename");
 
 #if defined(__APPLE__) && defined(__MACH__)
+    const char *filename = qdict_get_str(options, "filename");
+
     if (strstart(filename, "/dev/cdrom", NULL)) {
         kern_return_t kernResult;
         io_iterator_t mediaIterator;
@@ -2113,16 +2137,6 @@ static int hdev_open(BlockDriverState *bs, QDict *options, int flags,
 #endif
 
     s->type = FTYPE_FILE;
-#if defined(__linux__)
-    {
-        char resolved_path[ MAXPATHLEN ], *temp;
-
-        temp = realpath(filename, resolved_path);
-        if (temp && strstart(temp, "/dev/sg", NULL)) {
-            bs->sg = 1;
-        }
-    }
-#endif
 
     ret = raw_open_common(bs, options, flags, 0, &local_err);
     if (ret < 0) {
@@ -2132,6 +2146,9 @@ static int hdev_open(BlockDriverState *bs, QDict *options, int flags,
         return ret;
     }
 
+    /* Since this does ioctl the device must be already opened */
+    bs->sg = hdev_is_sg(bs);
+
     if (flags & BDRV_O_RDWR) {
         ret = check_hdev_writable(s);
         if (ret < 0) {
-- 
1.7.10.4