[ndctl PATCH] util: distinguish error codes for sysfs_{read, write}_attr()

[ndctl PATCH] util: distinguish error codes for sysfs_{read, write}_attr()

[Dan Williams]

There are occasions where it would be good to know the difference
between a sysfs attribute failing to be accessed because we could not
open versus could not read/write.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 util/sysfs.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/util/sysfs.c b/util/sysfs.c
index 31d1a898eba2..7905455890dc 100644
--- a/util/sysfs.c
+++ b/util/sysfs.c
@@ -34,13 +34,13 @@ int __sysfs_read_attr(struct log_ctx *ctx, const char *path, char *buf)
 
 	if (fd < 0) {
 		log_dbg(ctx, "failed to open %s: %s\n", path, strerror(errno));
-		return -1;
+		return -ENOENT;
 	}
 	n = read(fd, buf, SYSFS_ATTR_SIZE);
 	close(fd);
 	if (n < 0 || n >= SYSFS_ATTR_SIZE) {
 		log_dbg(ctx, "failed to read %s: %s\n", path, strerror(errno));
-		return -1;
+		return -EIO;
 	}
 	buf[n] = 0;
 	if (n && buf[n-1] == '\n')
@@ -56,7 +56,7 @@ static int write_attr(struct log_ctx *ctx, const char *path,
 
 	if (fd < 0) {
 		log_dbg(ctx, "failed to open %s: %s\n", path, strerror(errno));
-		return -1;
+		return -ENOENT;
 	}
 	n = write(fd, buf, len);
 	close(fd);
@@ -64,7 +64,7 @@ static int write_attr(struct log_ctx *ctx, const char *path,
 		if (!quiet)
 			log_dbg(ctx, "failed to write %s to %s: %s\n", buf, path,
 					strerror(errno));
-		return -1;
+		return -EIO;
 	}
 	return 0;
 }

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Re: [ndctl PATCH] util: distinguish error codes for sysfs_{read, write}_attr()

[Linda Knippers]

On 06/09/2017 01:27 AM, Dan Williams wrote:
> There are occasions where it would be good to know the difference
> between a sysfs attribute failing to be accessed because we could not
> open versus could not read/write.

I think it would be really helpful if you returned the actual errno value
rather than something hard coded.  The most common reason for not being able to write
something is that it requires running as root, in which case you should
get an EPERM. I think an accurate errno will help users figure out what's
gone wrong.

-- ljk

> 
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  util/sysfs.c |    8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/util/sysfs.c b/util/sysfs.c
> index 31d1a898eba2..7905455890dc 100644
> --- a/util/sysfs.c
> +++ b/util/sysfs.c
> @@ -34,13 +34,13 @@ int __sysfs_read_attr(struct log_ctx *ctx, const char *path, char *buf)
>  
>  	if (fd < 0) {
>  		log_dbg(ctx, "failed to open %s: %s\n", path, strerror(errno));
> -		return -1;
> +		return -ENOENT;
>  	}
>  	n = read(fd, buf, SYSFS_ATTR_SIZE);
>  	close(fd);
>  	if (n < 0 || n >= SYSFS_ATTR_SIZE) {
>  		log_dbg(ctx, "failed to read %s: %s\n", path, strerror(errno));
> -		return -1;
> +		return -EIO;
>  	}
>  	buf[n] = 0;
>  	if (n && buf[n-1] == '\n')
> @@ -56,7 +56,7 @@ static int write_attr(struct log_ctx *ctx, const char *path,
>  
>  	if (fd < 0) {
>  		log_dbg(ctx, "failed to open %s: %s\n", path, strerror(errno));
> -		return -1;
> +		return -ENOENT;
>  	}
>  	n = write(fd, buf, len);
>  	close(fd);
> @@ -64,7 +64,7 @@ static int write_attr(struct log_ctx *ctx, const char *path,
>  		if (!quiet)
>  			log_dbg(ctx, "failed to write %s to %s: %s\n", buf, path,
>  					strerror(errno));
> -		return -1;
> +		return -EIO;
>  	}
>  	return 0;
>  }
> 
> _______________________________________________
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> Linux-nvdimm@lists.01.org
> https://lists.01.org/mailman/listinfo/linux-nvdimm
> 

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Re: [ndctl PATCH] util: distinguish error codes for sysfs_{read, write}_attr()

[Dan Williams]

On Fri, Jun 9, 2017 at 1:09 PM, Linda Knippers <linda.knippers@hpe.com> wrote:
> On 06/09/2017 01:27 AM, Dan Williams wrote:
>> There are occasions where it would be good to know the difference
>> between a sysfs attribute failing to be accessed because we could not
>> open versus could not read/write.
>
> I think it would be really helpful if you returned the actual errno value
> rather than something hard coded.  The most common reason for not being able to write
> something is that it requires running as root, in which case you should
> get an EPERM. I think an accurate errno will help users figure out what's
> gone wrong.

Will do.
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