/**************************************************************/
/*  tpax: a topological pax implementation                    */
/*  Copyright (C) 2020--2024  SysDeer Technologies, LLC       */
/*  Released under GPLv2 and GPLv3; see COPYING.TPAX.         */
/**************************************************************/

#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <grp.h>
#include <pwd.h>
#include <sys/stat.h>

#include <tpax/tpax.h>
#include <tpax/tpax_specs.h>
#include "tpax_driver_impl.h"
#include "tpax_tmpfile_impl.h"
#include "tpax_errinfo_impl.h"

#ifndef ssizeof
#define ssizeof(x) (ssize_t)(sizeof(x))
#endif

int tpax_file_create_tmpfs_snapshot(
	const struct tpax_driver_ctx *  dctx,
	int                             fdat,
	const char *                    path,
	const struct stat *             srcst)
{
	int          fdsrc;
	int          fdtmp;
	char *       ch;
	ssize_t      nread;
	ssize_t      nbytes;
	ssize_t      ret;
	void *       buf;
	size_t       buflen;
	struct stat  dstst;

	/* record errors */
	tpax_driver_set_ectx(
		dctx,0,path);

	/* tmpfile */
	if ((fdtmp = tpax_tmpfile()) < 0)
		return TPAX_SYSTEM_ERROR(dctx);

	/* buffer */
	buf = tpax_get_driver_anon_map_addr(
		dctx,&buflen);

	/* open */
	if ((fdsrc = openat(fdat,path,O_CLOEXEC|O_NOCTTY|O_NOFOLLOW,0)) < 0) {
		close(fdtmp);
		return TPAX_SYSTEM_ERROR(dctx);
	}

	/* stat compare */
	if ((fstat(fdsrc,&dstst)) < 0) {
		close(fdsrc);
		close(fdtmp);
		return TPAX_SYSTEM_ERROR(dctx);

	} else if (tpax_util_stat_compare(srcst,&dstst)) {
		close(fdsrc);
		close(fdtmp);
		return TPAX_CUSTOM_ERROR(dctx,TPAX_ERR_FILE_CHANGED);
	}

	/* read/write loop */
	for (nread=0; nread<srcst->st_size; ) {
		nbytes = read(fdsrc,buf,buflen);

		while ((nbytes < 0) && (errno == EINTR))
			nbytes = read(fdsrc,buf,buflen);

		if (nbytes < 0) {
			close(fdsrc);
			close(fdtmp);
			return TPAX_SYSTEM_ERROR(dctx);

		} else if (nbytes == 0) {
			close(fdsrc);
			close(fdtmp);
			return TPAX_CUSTOM_ERROR(dctx,TPAX_ERR_FLOW_ERROR);

		} else {
			nread += nbytes;
		}

		for (ch=buf; nbytes; ch+=ret) {
			ret = write(fdtmp,ch,nbytes);

			while ((ret < 0) && (errno == EINTR))
				ret = write(fdtmp,ch,nbytes);

			if (ret < 0) {
				close(fdsrc);
				close(fdtmp);
				return TPAX_SYSTEM_ERROR(dctx);

			} else {
				nbytes -= ret;
			}
		}
	}

	/* stat compare */
	if ((fstat(fdsrc,&dstst)) < 0) {
		close(fdsrc);
		close(fdtmp);
		return TPAX_SYSTEM_ERROR(dctx);

	} else if (tpax_util_stat_compare(srcst,&dstst)) {
		close(fdsrc);
		close(fdtmp);
		return TPAX_CUSTOM_ERROR(dctx,TPAX_ERR_FILE_CHANGED);
	}

	/* yay */
	close(fdsrc);

	return fdtmp;
}