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| author | Karel Zak | 2016-04-19 12:39:05 +0200 |
|---|---|---|
| committer | Karel Zak | 2016-04-19 12:39:05 +0200 |
| commit | bfebe74e3babe8c188a51269acc2673f1aea283f (patch) | |
| tree | ea9ce1e6570d2286ba75ba4e25fc9680661f3270 /libblkid/src/probe.c | |
| parent | libblkid: make blkid_do_wipe() work with probes with offset (diff) | |
| download | kernel-qcow2-util-linux-bfebe74e3babe8c188a51269acc2673f1aea283f.tar.gz kernel-qcow2-util-linux-bfebe74e3babe8c188a51269acc2673f1aea283f.tar.xz kernel-qcow2-util-linux-bfebe74e3babe8c188a51269acc2673f1aea283f.zip | |
libblkid: reduce probing area for crazy CDROMs
Linux kernel reports devices greater than area readable by read(2).
The readable area is usually 2-3 CD blocks smaller (CD block is
2048-bytes) than size returned by BLKGETSIZE. This patch checks for
this issues to avoid I/O errors in probing functions.
Reported-by: Thomas Schmitt <scdbackup@gmx.net>
Signed-off-by: Karel Zak <kzak@redhat.com>
Diffstat (limited to 'libblkid/src/probe.c')
| -rw-r--r-- | libblkid/src/probe.c | 50 |
1 files changed, 49 insertions, 1 deletions
diff --git a/libblkid/src/probe.c b/libblkid/src/probe.c index 0c8625c57..0455c3797 100644 --- a/libblkid/src/probe.c +++ b/libblkid/src/probe.c @@ -752,6 +752,51 @@ int blkid_probe_is_cdrom(blkid_probe pr) return pr && (pr->flags & BLKID_FL_CDROM_DEV); } +static int is_sector_readable(int fd, uint64_t sector) +{ + char buf[512]; + ssize_t sz; + + if (blkid_llseek(fd, sector * 512, SEEK_SET) < 0) + goto failed; + + sz = read(fd, buf, sizeof(buf)); + if (sz != (ssize_t) sizeof(buf)) + goto failed; + + return 1; +failed: + DBG(LOWPROBE, ul_debug("CDROM: read sector %ju failed %m", sector)); + errno = 0; + return 0; +} + +/* + * Linux kernel reports (BLKGETSIZE) cdrom device size greater than area + * readable by read(2). We have to reduce the probing area to avoid unwanted + * I/O errors in probing functions. It seems that unreadable are always last 2 + * or 3 CD blocks (CD block size is 2048 bytes, it means 12 in 512-byte + * sectors). + */ +static void cdrom_size_correction(blkid_probe pr) +{ + uint64_t n, nsectors = pr->size >> 9; + + for (n = nsectors - 12; n < nsectors; n++) { + if (!is_sector_readable(pr->fd, n)) + goto failed; + } + + DBG(LOWPROBE, ul_debug("CDROM: full size available")); + return; +failed: + /* 'n' is the failed sector, reduce device size to n-1; */ + DBG(LOWPROBE, ul_debug("CDROM: reduce size from %ju to %ju.", + (uintmax_t) pr->size, + (uintmax_t) (n - 1) << 9)); + pr->size = n << 9; +} + /** * blkid_probe_set_device: * @pr: probe @@ -844,8 +889,11 @@ int blkid_probe_set_device(blkid_probe pr, int fd, else if (S_ISBLK(sb.st_mode) && !blkid_probe_is_tiny(pr) && blkid_probe_is_wholedisk(pr) && - ioctl(fd, CDROM_GET_CAPABILITY, NULL) >= 0) + ioctl(fd, CDROM_GET_CAPABILITY, NULL) >= 0) { + pr->flags |= BLKID_FL_CDROM_DEV; + cdrom_size_correction(pr); + } #endif DBG(LOWPROBE, ul_debug("ready for low-probing, offset=%"PRIu64", size=%"PRIu64"", |