xfs_io problem with pread

j.ski · 08-28-2016, 11:54 PM

I am using Fedora 23, updated to 4.6.7-200.fc23.x86_64, using:

j.ski@localhost ~> df -T
Filesystem Type 1K-blocks Used Available Use% Mounted on
devtmpfs devtmpfs 2912076 0 2912076 0% /dev
tmpfs tmpfs 2924296 143548 2780748 5% /dev/shm
tmpfs tmpfs 2924296 1692 2922604 1% /run
tmpfs tmpfs 2924296 0 2924296 0% /sys/fs/cgroup
/dev/mapper/fedora-root00 xfs 52403200 13214860 39188340 26% /
tmpfs tmpfs 2924296 80 2924216 1% /tmp
/dev/mapper/fedora-home00 xfs 566007784 10329884 555677900 2% /home
/dev/sda1 xfs 508580 201876 306704 40% /boot
tmpfs tmpfs 584860 20 584840 1% /run/user/42
tmpfs tmpfs 584860 24 584836 1% /run/user/1000

I am trying to use xfs_io to read the contents of a file:

$ xfs_io /home/j.ski/-.truste.com

xfs_io> p
[000] /home/j.ski/-.truste.com (xfs,non-sync,non-direct,read-write)

xfs_io> pread -v 100 /home/j.ski/-.truste.com
pread64: Bad address

When I first tried this I got what I assumed were the files contents. BUT the next time I tried the exact same command, I get:

xfs_io> pread -v 100 /home/j.ski/-.truste.com
pread64: Bad address

Any idea(s)?

norobro · 08-30-2016, 03:26 PM

Code:

xfs_io> help pread
pread [-b bs] [-v] [-i N] [-FBR [-Z N]] off len -- reads a number of bytes at a specified offset

 reads a range of bytes in a specified block size from the given offset

To read 100 bytes from the beginning of the file:

Code:

xfs_io> pread -v 0 100