diff options
| author | Zhongqiu Han <zhongqiu.han@oss.qualcomm.com> | 2025-11-07 15:45:33 +0800 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2025-11-10 16:23:13 -0800 |
| commit | 5b9192c2c075edf8a35f8c6c2b5ef36cdc8ce9f9 (patch) | |
| tree | 6b1935e98e75953fb1cbaa11d4bff962e0ce6e88 | |
| parent | 73edb26b06ea0eb5bd8c6cae5b2df212ae3c7ab5 (diff) | |
ptp: ocp: Document sysfs output format for backward compatibility
Add a comment to ptp_ocp_tty_show() explaining that the sysfs output
intentionally does not include a trailing newline. This is required for
backward compatibility with existing userspace software that reads the
sysfs attribute and uses the value directly as a device path.
A previous attempt to add a newline to align with common kernel
conventions broke userspace applications that were opening device paths
like "/dev/ttyS4\n" instead of "/dev/ttyS4", resulting in ENOENT errors.
This comment prevents future attempts to "fix" this behavior, which would
break existing userspace applications.
Link: https://lore.kernel.org/netdev/20251030124519.1828058-1-zhongqiu.han@oss.qualcomm.com/
Link: https://lore.kernel.org/netdev/aef3b850-5f38-4c28-a018-3b0006dc2f08@linux.dev/
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Zhongqiu Han <zhongqiu.han@oss.qualcomm.com>
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Link: https://patch.msgid.link/20251107074533.416048-1-zhongqiu.han@oss.qualcomm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
| -rw-r--r-- | drivers/ptp/ptp_ocp.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/drivers/ptp/ptp_ocp.c b/drivers/ptp/ptp_ocp.c index a5c363252986..eeebe4d149f7 100644 --- a/drivers/ptp/ptp_ocp.c +++ b/drivers/ptp/ptp_ocp.c @@ -3430,6 +3430,12 @@ ptp_ocp_tty_show(struct device *dev, struct device_attribute *attr, char *buf) struct dev_ext_attribute *ea = to_ext_attr(attr); struct ptp_ocp *bp = dev_get_drvdata(dev); + /* + * NOTE: This output does not include a trailing newline for backward + * compatibility. Existing userspace software uses this value directly + * as a device path (e.g., "/dev/ttyS4"), and adding a newline would + * break those applications. Do not add a newline to this output. + */ return sysfs_emit(buf, "ttyS%d", bp->port[(uintptr_t)ea->var].line); } |