Subject: Re: [PATCH/WIP 1/8] wrapper: implement xopen()

From: Torsten Bögershausen <[email-masked]>
Date: Wed, 27 May 2015 21:03:47 +0200

On 2015-05-27 15.33, Paul Tan wrote:
> A common usage pattern of open() is to check if it was successful, and
> die() if it was not:
> 
> 	int fd = open(path, O_WRONLY | O_CREAT, 0777);
> 	if (fd < 0)
> 		die_errno(_("Could not open '%s' for writing."), path);
> 
> Implement a wrapper function xopen() that does the above so that we can
> save a few lines of code, and make the die() messages consistent.
> 
> Signed-off-by: Paul Tan <[email-masked]>
> ---
>  git-compat-util.h |  1 +
>  wrapper.c         | 18 ++++++++++++++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/git-compat-util.h b/git-compat-util.h
> index 17584ad..9745962 100644
> --- a/git-compat-util.h
> +++ b/git-compat-util.h
> @@ -718,6 +718,7 @@ extern char *xstrndup(const char *str, size_t len);
>  extern void *xrealloc(void *ptr, size_t size);
>  extern void *xcalloc(size_t nmemb, size_t size);
>  extern void *xmmap(void *start, size_t length, int prot, int flags, int fd, off_t offset);
> +extern int xopen(const char *path, int flags, mode_t mode);
>  extern ssize_t xread(int fd, void *buf, size_t len);
>  extern ssize_t xwrite(int fd, const void *buf, size_t len);
>  extern ssize_t xpread(int fd, void *buf, size_t len, off_t offset);
> diff --git a/wrapper.c b/wrapper.c
> index c1a663f..971665a 100644
> --- a/wrapper.c
> +++ b/wrapper.c
> @@ -189,6 +189,24 @@ void *xcalloc(size_t nmemb, size_t size)
>  # endif
>  #endif
>  
The original open can take 2 or 3 parameters, how about this:
int xopen(const char *path, int oflag, ... )
{
        va_list params;
        int mode;
        int fd;

        va_start(params, oflag);
        mode = va_arg(params, int);
        va_end(params);

        fd = open(path, oflag, mode);

> +/**
> + * xopen() is the same as open(), but it die()s if the open() fails.
> + */
> +int xopen(const char *path, int flags, mode_t mode)
> +{
> +	int fd;
> +
> +	assert(path);
> +	fd = open(path, flags, mode);
> +	if (fd < 0) {
> +		if ((flags & O_WRONLY) || (flags & O_RDWR))
> +			die_errno(_("could not open '%s' for writing"), path);
This is only partly true:
it could be either "writing" or "read write".
I don't know if the info "for reading" or "for writing" is needed/helpful at all,
or if a simple "could not open" would be enough.

Another thing:
should we handle EINTR ?
(Somewhere in the back of my head I remember that some OS
 returned EINTR when handling some foreign file system
 Mac OS / NTFS ?)