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open_by_handle_at.2: Rework example programs 

Rework example programs so that they use a text file (rather
than a binary file) to exchange mount ID and file handle.
Various clean-ups and bug fixes after review by Mike Frysinger.

Reviewed-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2014-03-19 14:08:54 +01:00
parent 886f35af61
commit 3ad5d1b9f6
1 changed files with 66 additions and 44 deletions
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110
man2/open_by_handle_at.2
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@ -360,7 +360,7 @@ and later used in a different process that calls
.BR open_by_handle_at ().
Some filesystem don't support the translation of pathnames to
file handles, for example,
file handles, for example,
.IR /proc ,
.IR /sys ,
and various network filesystems.
@ -491,7 +491,7 @@ no longer exists.
.in +4n
.nf
$ \fBstat \-\-printf="%i\\n" cecilia.txt\fP # Display inode number
$ \fBstat \-\-printf="%i\\n" cecilia.txt\fP # Display inode number
4072121
$ \fBrm cecilia.txt\fP
$ \fBecho 'Can you please think about it?' > cecilia.txt\fP
@ -521,16 +521,19 @@ int
main(int argc, char *argv[])
{
struct file_handle *fhp;
int mount_id, fhsize, s;
int mount_id, fhsize, flags, dirfd, j;
char *pathname;
if (argc < 2 || strcmp(argv[1], "\-\-help") == 0) {
if (argc != 2) {
fprintf(stderr, "Usage: %s pathname\\n", argv[0]);
exit(EXIT_FAILURE);
}
pathname = argv[1];
/* Allocate file_handle structure */
fhsize = sizeof(struct file_handle *);
fhsize = sizeof(*fhp);
fhp = malloc(fhsize);
if (fhp == NULL)
errExit("malloc");
@ -538,9 +541,11 @@ main(int argc, char *argv[])
/* Make an initial call to name_to_handle_at() to discover
the size required for file handle */
dirfd = AT_FDCWD; /* For name_to_handle_at() calls */
flags = 0; /* For name_to_handle_at() calls */
fhp\->handle_bytes = 0;
s = name_to_handle_at(AT_FDCWD, argv[1], fhp, &mount_id, 0);
if (s != \-1 || errno != EOVERFLOW) {
if (name_to_handle_at(dirfd, pathname, fhp,
&mount_id, flags) != \-1 || errno != EOVERFLOW) {
fprintf(stderr, "Unexpected result from name_to_handle_at()\\n");
exit(EXIT_FAILURE);
}
@ -554,18 +559,17 @@ main(int argc, char *argv[])
/* Get file handle from pathname supplied on command line */
if (name_to_handle_at(AT_FDCWD, argv[1], fhp, &mount_id, 0) == \-1)
if (name_to_handle_at(dirfd, pathname, fhp, &mount_id, flags) == \-1)
errExit("name_to_handle_at");
/* Write mount ID, file handle size, and file handle to stdout,
for later reuse by t_open_by_handle_at.c */
if (write(STDOUT_FILENO, &mount_id, sizeof(int)) != sizeof(int) ||
write(STDOUT_FILENO, &fhsize, sizeof(int)) != sizeof(int) ||
write(STDOUT_FILENO, fhp, fhsize) != fhsize) {
fprintf(stderr, "Write failure\\n");
exit(EXIT_FAILURE);
}
printf("%d\\n", mount_id);
printf("%d %d ", fhp\->handle_bytes, fhp\->handle_type);
for (j = 0; j < fhp\->handle_bytes; j++)
printf(" %02x", fhp\->f_handle[j]);
printf("\\n");
exit(EXIT_SUCCESS);
}
@ -598,85 +602,102 @@ open_mount_path_by_id(int mount_id)
char *linep;
size_t lsize;
char mount_path[PATH_MAX];
int fmnt_id, fnd, nread;
int mi_mount_id, found;
ssize_t nread;
FILE *fp;
fp = fopen("/proc/self/mountinfo", "r");
fp = fopen("/proc/self/mountinfo", "r");
if (fp == NULL)
errExit("fopen");
for (fnd = 0; !fnd ; ) {
linep = NULL;
found = 0;
linep = NULL;
while (!found) {
nread = getline(&linep, &lsize, fp);
if (nread == \-1)
break;
nread = sscanf(linep, "%d %*d %*s %*s %s", &fmnt_id, mount_path);
nread = sscanf(linep, "%d %*d %*s %*s %s",
&mi_mount_id, mount_path);
if (nread != 2) {
fprintf(stderr, "Bad sscanf()\\n");
exit(EXIT_FAILURE);
}
free(linep);
if (fmnt_id == mount_id)
fnd = 1;
if (mi_mount_id == mount_id)
found = 1;
}
free(linep);
fclose(fp);
if (!fnd) {
if (!found) {
fprintf(stderr, "Could not find mount point\\n");
exit(EXIT_FAILURE);
}
return open(mount_path, O_RDONLY | O_DIRECTORY);
return open(mount_path, O_RDONLY);
}
int
main(int argc, char *argv[])
{
struct file_handle *fhp;
int mount_id, fd, mount_fd, fhsize;
int mount_id, fd, mount_fd, handle_bytes, j;
ssize_t nread;
#define BSIZE 1000
char buf[BSIZE];
char buf[1000];
#define LINE_SIZE 100
char line1[LINE_SIZE], line2[LINE_SIZE];
char *nextp;
if (argc > 1 && strcmp(argv[1], "\-\-help") == 0) {
fprintf(stderr, "Usage: %s [mount\-dir]]\\n",
argv[0]);
if ((argc > 1 && strcmp(argv[1], "\-\-help") == 0) || argc > 2) {
fprintf(stderr, "Usage: %s [mount\-path]\\n", argv[0]);
exit(EXIT_FAILURE);
}
/* Read data produced by t_name_to_handle_at.c */
/* Standard input contains mount ID and file handle information:
if (read(STDIN_FILENO, &mount_id, sizeof(int)) != sizeof(int))
errExit("read");
Line 1: <mount_id>
Line 2: <handle_bytes> <handle_type> <bytes of handle in hex>
*/
if (read(STDIN_FILENO, &fhsize, sizeof(int)) != sizeof(int))
errExit("read");
if ((fgets(line1, sizeof(line1), stdin) == NULL) ||
(fgets(line2, sizeof(line2), stdin) == NULL)) {
fprintf(stderr, "Missing mount_id / file handle\\n");
exit(EXIT_FAILURE);
}
fhp = malloc(fhsize);
mount_id = atoi(line1);
handle_bytes = strtoul(line2, &nextp, 0);
/* Given handle_bytes, we can now allocate file_handle structure */
fhp = malloc(sizeof(struct file_handle) + handle_bytes);
if (fhp == NULL)
errExit("malloc");
if (read(STDIN_FILENO, fhp, fhsize) != fhsize)
errExit("read");
fhp\->handle_bytes = handle_bytes;
fhp\->handle_type = strtoul(nextp, &nextp, 0);
for (j = 0; j < fhp\->handle_bytes; j++)
fhp\->f_handle[j] = strtoul(nextp, &nextp, 16);
/* Obtain file descriptor for mount point, either by opening
the pathname specified on the command line, or by scanning
/proc/self/mounts to find a mount that matches the \(aqmount_id\(aq
obtained by name_to_handle_at() (in t_name_to_handle_at.c) */
that we received from stdin. */
if (argc > 1)
mount_fd = open(argv[1], O_RDONLY | O_DIRECTORY);
mount_fd = open(argv[1], O_RDONLY);
else
mount_fd = open_mount_path_by_id(mount_id);
if (mount_fd == \-1)
errExit("opening mount fd");
/* Open name using handle and mount point */
/* Open file using handle and mount point */
fd = open_by_handle_at(mount_fd, fhp, O_RDONLY);
if (fd == \-1)
@ -684,10 +705,11 @@ main(int argc, char *argv[])
/* Try reading a few bytes from the file */
nread = read(fd, buf, BSIZE);
nread = read(fd, buf, sizeof(buf));
if (nread == \-1)
errExit("read");
printf("Read %ld bytes\\n", (long) nread);
printf("Read %zd bytes\\n", nread);
exit(EXIT_SUCCESS);
}