If scsi-generic driver is in use, an SG node can be specified in the command line in place of a regular SCSI device. In this case, sg_get_max_segments() fails to open max_segments entry in sysfs because /dev/sgX is a character device. As the result, the maximum transfer size for the device may be calculated incorrectly, causing I/O errors if the maximum transfer size at the guest ends up to be larger compared to the host.
Check system device type in sg_get_max_segments() and read the max_segments value differently if it is a character device. Reported-by: Johannes Thumshirn <johannes.thumsh...@wdc.com> Fixes: 9103f1ceb46614b150bcbc3c9a4fbc72b47fedcc Signed-off-by: Dmitry Fomichev <dmitry.fomic...@wdc.com> --- block/file-posix.c | 55 +++++++++++++++++++++++++++------------------- 1 file changed, 32 insertions(+), 23 deletions(-) diff --git a/block/file-posix.c b/block/file-posix.c index 094e3b0212..f9e2424e8f 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -1108,6 +1108,7 @@ static int sg_get_max_segments(int fd) int ret; int sysfd = -1; long max_segments; + unsigned int max_segs; struct stat st; if (fstat(fd, &st)) { @@ -1115,30 +1116,38 @@ static int sg_get_max_segments(int fd) goto out; } - 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; + if (S_ISBLK(st.st_mode)) { + 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; + } + do { + ret = read(sysfd, buf, sizeof(buf) - 1); + } while (ret == -1 && errno == EINTR); + 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; + } + } else { + ret = ioctl(fd, SG_GET_SG_TABLESIZE, &max_segs); + if (ret != 0) { + ret = -errno; + goto out; + } + ret = max_segs; } - do { - ret = read(sysfd, buf, sizeof(buf) - 1); - } while (ret == -1 && errno == EINTR); - 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); -- 2.21.0