[PATCH RFC 2/3] libfile: implement read_fd counterpart to read_file

[Ahmad Fatoum]

On 21.11.23 08:36, Sascha Hauer wrote:
> On Mon, Nov 20, 2023 at 09:37:49AM +0100, Ahmad Fatoum wrote:
>> Files opened with O_TMPFILE have no name, so read_file can't be used
>> with them. Therefore add a read_fd function, which slurps all a file's
>> contents into a buffer.
>>
>> Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
>> ---
>>  include/libfile.h |  2 ++
>>  lib/libfile.c     | 44 ++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 46 insertions(+)
>>
>> diff --git a/include/libfile.h b/include/libfile.h
>> index a353ccfa9ea9..423e7ffec5b7 100644
>> --- a/include/libfile.h
>> +++ b/include/libfile.h
>> @@ -12,6 +12,8 @@ char *read_file_line(const char *fmt, ...);
>>  
>>  void *read_file(const char *filename, size_t *size);
>>  
>> +void *read_fd(int fd, size_t *size);
>> +
>>  int read_file_2(const char *filename, size_t *size, void **outbuf,
>>  		loff_t max_size);
>>  
>> diff --git a/lib/libfile.c b/lib/libfile.c
>> index e53ba08415a2..c257baaa2733 100644
>> --- a/lib/libfile.c
>> +++ b/lib/libfile.c
>> @@ -306,6 +306,50 @@ void *read_file(const char *filename, size_t *size)
>>  }
>>  EXPORT_SYMBOL(read_file);
>>  
>> +/**
>> + * read_fd - read from a file descriptor to an allocated buffer
>> + * @filename:  The file descriptor to read
>> + * @size:      After successful return contains the size of the file
>> + *
>> + * This function reads a file descriptor from offset 0 until EOF to an
>> + * allocated buffer.
>> + *
>> + * Return: The buffer containing the file or NULL on failure
>> + */
>> +void *read_fd(int fd, size_t *out_size)
>> +{
>> +	off_t off;
>> +	ssize_t ret;
>> +	size_t size;
>> +	void *buf;
>> +
>> +	off = lseek(fd, SEEK_CUR, 0);
> 
> You lseek to the current position. It seems you are trying to determine
> the size of the file, so did you mean to use SEEK_END?
> 
> You could use fstat() instead. With that you could also correctly handle
> FILE_SIZE_STREAM.

Will use fstat, thanks.

> 
>> +	if (off >= 0) {
>> +		size = off;
>> +		off = lseek(fd, SEEK_SET, 0);
>> +	}
>> +	if (off < 0) {
>> +		ret = off;
>> +		goto close_fd;
>> +	}
>> +
>> +	buf = malloc(size + 3);
>> +	ret = read_full(fd, buf, size);
> 
> You can use pread_full() here to avoid having to lseek to the beginning
> of the file.

Ok, will do.

> 
>> +	if (ret < 0) {
>> +		free(buf);
>> +		goto close_fd;
>> +	}
>> +
>> +	memset(&buf[size], '\0', 3);
>> +	*out_size = size;
>> +
>> +close_fd:
>> +	close(fd);
>> +
>> +	return ret < 0 ? NULL : buf;
> 
> Return an error pointer or an error integer and pass buf as argument?

I want it to return a buffer like read_file does. I think that would
be the least surprising API.

Cheers,
Ahmad

> 
> Sascha
> 

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