我正在尝试几个小时来执行以下任务。但它仍然没有用，我真的不知道了。
任务：
如果在命令行或程序中传递参数-s，则列出当前目录中所有稀疏文件的c程序应该打印已经代表文件中的间隙的磁盘块数和磁盘块数如果您使用-c而不是-s。
代码：
int main(int argc, char* argv[]) {
if(argc > 3) {
fprintf(stderr,"usage: sparse-files [-s|-c <file name>]\n");
exit(EXIT_FAILURE);
}
DIR *dirp;
struct dirent *dp;
struct stat st = {0};
int option, sflag = 0, cflag = 0;
if ((dirp = opendir(".")) == NULL)
perror("Could not open '.'");
while((option = getopt(argc, argv,"sc:")) != -1) {
switch(option) {
case 'c':
cflag = 1;
break;
case 's':
sflag = 1;
break;
default:
break;
}
}
off_t sz;
while((dp = readdir(dirp)) != NULL) {
int counter = 0, counter2 = 0;
if(dp->d_type == DT_REG) {
if (sflag) {
char * file = dp->d_name;
if(stat(file, &st) == -1)
perror("stat()");
sz = (st.st_size + st.st_blksize -1) & ~st.st_blksize;
if ((st.st_blocks * st.st_blksize) < sz)
printf("%s\n", dp->d_name);
} else if (cflag) {
char * file = dp->d_name;
if(stat(file, &st) == -1)
perror("stat()");
int fd = open(file, O_RDONLY);
sz = (st.st_size + st.st_blksize -1) & ~st.st_blksize;
if ((st.st_blocks * st.st_blksize) < sz) {
while(lseek(fd, 0, SEEK_HOLE) != -1)
counter++;
while(lseek(fd, 0, SEEK_DATA) != -1)
counter2++;
printf("%d %d %s\n", counter, counter2, file);
close(fd);
}
}
}
closedir(dirp);
return 0;
}
我真的不知道如何处理它。我真的希望有人可以提供帮助。
答案 0 :(得分：3)
您可能知道，在调用 stat()时返回struct stat info，info.st_size是文件的总大小（以字节为单位），info.st_blocks*512是数字存储在磁盘上的字节数。
在Linux中，文件系统以info.st_blksize字节的对齐块存储数据。 （这也意味着info.st_blocks*512可以大于info.st_size（最多info.st_blksize-1个字节）。如果文件稀疏，它也可以更小。）
未存储的数据（稀疏文件中的漏洞）和显式归零的存储数据都读为零。
如果您想知道文件中有多少零填充块，则需要读取整个文件。使用大小为info.st_blksize字节的整数倍的缓冲区。对于每个st_blksize字节的对齐块，检查它们是否全为零。令总块数（包括最后一个可能的部分块）为total_blocks，并且所有零内容的块数为zero_blocks。
struct stat info;
/* Number of filesystem blocks for the file */
total_blocks = info.st_size / info.st_blksize
+ (info.st_size % info.st_blksize) ? 1 : 0;
/* Number of bytes stored for the file */
stored_bytes = 512 * info.st_blocks;
/* Number of filesystem blocks used for file data */
stored_blocks = stored_bytes / info.st_blksize
+ (stored_bytes % info.st_blksize) ? 1 : 0;
/* Number of sparse blocks */
sparse_blocks = total_blocks - stored_blocks;
/* TODO: count zero_blocks,
* by reading file in info.st_blksize chunks,
* and saving the number of all-zero chunks
* in zero_blocks. */
/* Number of stored zero blocks */
zeroed_blocks = zero_blocks - sparse_blocks;
转换为字节，你有
info.st_size是以字节为单位的文件大小stored_blocks*info.st_blksize是磁盘上使用的字节数sparse_blocks*info.st_blksize是磁盘上稀疏孔中的字节数zeroed_blocks*info.st_blksize是磁盘上不必要存储的零字节数;可以存储为稀疏孔而不是请注意，您可以使用cp --sparse=always --preserve=all SOURCEFILE TARGETFILE创建文件的相同副本，但“优化”稀疏性，以便将足够长的零字节运行存储为孔;这可以帮助您测试您的程序。有关详细信息，请参阅man 1 cp。您还可以使用dd if=/dev/zero of=TARGETFILE bs=BLOCKSIZE count=BLOCKS创建长序列的零;有关详细信息，请参阅man 1 dd和man 4 null。
编辑添加：
这是一个示例函数examine()，用于打开指定文件，获取统计信息，如果需要（即请求不必要存储的零的数量），则读取整个文件。
我只是对它进行了轻微的测试，但它应该实现上面的逻辑。
非常粗糙;我最关注正确的错误检查和动态内存分配/释放的正确性。 （它应该检查并返回所有错误条件，甚至是一些永远不会发生的错误条件，并且永远不会泄漏内存。也就是说，除非我在代码中有错误或思考，否则非常欢迎更正。）
最好将其拆分为更小，更易于管理的功能。
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdint.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>
/* Return nonzero if the buffer is all zeros.
*/
static inline int is_zero(const void *const ptr, const size_t len)
{
const char *p = (const char *)ptr;
const char *const q = (const char *const)ptr + len;
while (p < q)
if (*(p++))
return 0;
return 1;
}
/* Return 0 if success, errno error code otherwise.
* (*sizeptr): File size in bytes
* (*blocksizeptr): File block size in bytes
* (*storedptr): Bytes stored on disk
* (*sparseptr): Bytes in sparse holes
* (*zeroedptr): Unnecessarily stored zero bytes
* If zeroedptr is NULL, the file is only opened and
* statistics obtained via fstat(). Otherwise, the entire
* file will be read.
* Special errors:
* EINVAL: NULL or empty file name
* EISDIR: Name refers to a directory
* EISNAM: Name refers to a pipe or device
* EBUSY: File was modified during read
*/
int examine(const char *const filename,
uint64_t *const sizeptr,
uint64_t *const blocksizeptr,
uint64_t *const storedptr,
uint64_t *const sparseptr,
uint64_t *const zeroedptr)
{
struct stat info;
int fd, result;
size_t size, have;
uint64_t total, nonzero, stored;
int cause = 0;
char *data = NULL;
/* Check for NULL or empty filename. */
if (!filename || !*filename)
return errno = EINVAL;
/* Open the specified file. */
do {
fd = open(filename, O_RDONLY | O_NOCTTY);
} while (fd == -1 && errno == EINTR);
if (fd == -1)
return errno;
do {
/* Obtain file statistics. */
if (fstat(fd, &info) == -1) {
cause = errno;
break;
}
/* Count total, rounding up to next multiple of block size. */
total = (uint64_t)info.st_size;
if (total % (uint64_t)info.st_blksize)
total += (uint64_t)info.st_blksize - ((uint64_t)total % (uint64_t)info.st_blksize);
/* Count total stored bytes. */
stored = (uint64_t)512 * (uint64_t)info.st_blocks;
/* Fill in immediately known fields. */
if (sizeptr)
*sizeptr = (uint64_t)info.st_size;
if (blocksizeptr)
*blocksizeptr = (uint64_t)info.st_blksize;
if (storedptr)
*storedptr = stored;
if (sparseptr) {
if (total > stored)
*sparseptr = total - stored;
else
*sparseptr = 0;
}
if (zeroedptr)
*zeroedptr = 0;
/* Verify we have a regular file. */
if (S_ISDIR(info.st_mode)) {
cause = EISDIR;
break;
} else
if (!S_ISREG(info.st_mode)) {
cause = EISNAM;
break;
}
/* Verify we have a valid block size. */
if (info.st_blksize < (blksize_t)1) {
cause = ENOTSUP;
break;
}
/* If zeroedptr is NULL, we do not need to read the file. */
if (!zeroedptr) {
/* Close descriptor and return success. */
do {
result = close(fd);
} while (result == -1 && errno == EINTR);
if (result == -1)
return errno;
return 0;
}
/* Use large enough chunks for I/O. */
if (info.st_blksize < (blksize_t)131072) {
const size_t chunks = (size_t)131072 / (size_t)info.st_blksize;
size = chunks * (size_t)info.st_blksize;
} else
size = (size_t)info.st_blksize;
/* Allocate buffer. */
data = malloc(size);
if (!data) {
cause = ENOMEM;
break;
}
/* Clear counters. */
total = 0;
nonzero = 0;
have = 0;
/* Read loop. */
while (1) {
size_t i;
ssize_t bytes;
int ended = 0;
while (have < (size_t)info.st_blksize) {
bytes = read(fd, data + have, size - have);
if (bytes > (ssize_t)0) {
have += bytes;
total += (uint64_t)bytes;
} else
if (bytes == (ssize_t)0) {
/* Clear the end of the buffer; just to be sure */
memset(data + have, 0, size - have);
ended = 1;
break;
} else
if (bytes != (ssize_t)-1) {
cause = EIO;
break;
} else
if (errno != EINTR) {
cause = errno;
break;
}
}
if (cause)
break;
/* Count number of zero/nonzero chunks in buffer, but add up as bytes. */
i = have / (size_t)info.st_blksize;
while (i-->0)
if (!is_zero(data + i * (size_t)info.st_blksize, (size_t)info.st_blksize))
nonzero += (uint64_t)info.st_blksize;
/* Followed by a partial chunk? */
{ const size_t overlap = have % (size_t)info.st_blksize;
if (overlap) {
if (have > overlap)
memcpy(data, data + have - overlap, overlap);
have = overlap;
} else
have = 0;
}
/* Next round of the loop, unless end of input. */
if (!ended)
continue;
/* Entire file has been processed. */
/* Partial chunk in buffer? */
if (have) {
if (!is_zero(data, have))
nonzero += (uint64_t)info.st_blksize;
}
/* If file size changed, update statistics. */
if (total != (uint64_t)info.st_size) {
if (fstat(fd, &info) == -1) {
cause = errno;
break;
}
/* File changed from under us? */
if (total != (uint64_t)info.st_size) {
cause = EBUSY;
break;
}
}
/* Align total size to (next) multiple of block size. */
if (total % (uint64_t)info.st_blksize)
total += (uint64_t)info.st_blksize - (total % (uint64_t)info.st_blksize);
/* Bytes stored on disk. */
stored = (uint64_t)512 * (uint64_t)info.st_blocks;
/* Sanity check. (File changed while we read it?) */
if (stored > total || nonzero > stored) {
cause = EBUSY;
break;
}
/* Update fields. */
if (sizeptr)
*sizeptr = (uint64_t)info.st_size;
if (storedptr)
*storedptr = (uint64_t)512 * (uint64_t)info.st_blocks;
if (sparseptr)
*sparseptr = total - stored;
if (zeroedptr)
*zeroedptr = (total - nonzero) - (total - stored);
/* Discard buffer. */
free(data);
/* Close file and return. */
do {
result = close(fd);
} while (result == -1 && errno == EINTR);
if (result == -1)
return errno;
return 0;
}
} while (0);
/* Free buffer, if allocated. free(NULL) is safe. */
free(data);
/* Close file, and return with cause. */
do {
result = close(fd);
} while (result == -1 && errno == EINTR);
return errno = cause;
}
为了便于携带，所有返回参数都是64位无符号整数，
并以字节为单位指定相应的大小。请注意，(*storedptr)+(*sparseptr)定义了向上舍入为(*blocksizeptr)的下一个倍数的总字节数。 (*zeroesptr)仅包含显式存储的零，而不包括稀疏空洞。再次，将(*zeroesptr)视为不必要存储的零的数量。
我使用rm -f test ; dd if=/dev/zero of=test bs=10000 seek=3 count=1生成一个test文件，其中包含30,000个字节的孔，后跟10,000个零。 examine()会返回size=40000，blocksize=4096，stored=12288，sparse=28672，zeroed=12288，这对我来说是正确的。
有问题吗？