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    SubjectError returns not handled correctly by sysfs.c:subsys_attr_store()
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    The buf in fs/sysfs.c:subsys_attr_store() does not seem to be updated
    correctly when returning a negative value (indicating that an error
    condition has occurred) is returned. If a negative value is returned,
    the next subsequent call to subsys_attr_store will have the contents of
    buf appended to the previous call. Example: I have modified the
    sd.c:sd_store_allow_restart to always print out the contents of the buf
    and return an error using the following patch:

    --- a/drivers/scsi/sd.c
    +++ b/drivers/scsi/sd.c
    @@ -183,6 +183,9 @@ static ssize_t sd_store_allow_restart(struct class_device *c
    struct scsi_disk *sdkp = to_scsi_disk(cdev);
    struct scsi_device *sdp = sdkp->device;

    + printk(KERN_ERR "buf_ptr = 0x%p, buf = %s, count = %u\n", buf, buf, coun
    + return -EINVAL;
    +
    if (!capable(CAP_SYS_ADMIN))
    return -EACCES;

    I get the following output when writing invalid values to the
    allow_restart sysfs file:
    # echo x > /sys/class/scsi_disk/4:0:0:0/allow_restart
    bash: echo: write error: Invalid argument
    # echo y > /sys/class/scsi_disk/4:0:0:0/allow_restart
    bash: echo: write error: Invalid argument
    # echo z > /sys/class/scsi_disk/4:0:0:0/allow_restart
    bash: echo: write error: Invalid argument
    And the console output shows:

    buf_ptr = 0xe00001004bdb0000, buf = x
    , count = 2
    buf_ptr = 0xe00001004bdb0000, buf = x
    , count = 2
    buf_ptr = 0xe00001004bdb0000, buf = x
    y
    , count = 4
    buf_ptr = 0xe00001004bdb0000, buf = x
    y
    , count = 4
    buf_ptr = 0xe00001004caf0000, buf = x
    y
    z
    , count = 6
    buf_ptr = 0xe00001004caf0000, buf = x
    y
    z
    , count = 6
    and the same append problem occurs when using another sysfs file:

    # echo xyzzy > /sys/class/scsi_disk/4:0:1:0/allow_restart
    bash: echo: write error: Invalid argument
    buf_ptr = 0xe00001004caf0000, buf = x
    y
    z
    xyzzy
    , count = 12
    I found this problem in 2.6.24-rc3 and and an earlier version of 2.6.23.

    This seems to work correctly on 2.6.18 (at least with the RHEL5 kernel I
    did some testing with), i.e. the contents of buf from the previous
    failed called are thrown away/overwritten. I looked through sysfs.c to
    see if I could find anything obvious but could not see anything.
    Perhaps this is handled at a higher level.

    --
    Andrew Patterson
    Hewlett-Packard

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