uml: Fix which_tmpdir failure when /dev/shm is a symlink, and in other edge cases
which_tmpdir did the wrong thing if /dev/shm was a symlink (e.g., to /run/shm), if there were multiple mounts on top of each other, if the mount(s) were obscured by a later mount, or if /dev/shm was a prefix of another mount point. This fixes these cases. Applies to 3.9.6. Signed-off-by: Tristan Schmelcher <tschmelcher@google.com> Signed-off-by: Richard Weinberger <richard@nod.at>
This commit is contained in:
Tristan Schmelcher
Richard Weinberger
parent
0974a9cadc
commit
7473534130
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@ -52,6 +52,25 @@ static void __init find_tempdir(void)
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strcat(tempdir, "/");
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}
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/*
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* Remove bytes from the front of the buffer and refill it so that if there's a
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* partial string that we care about, it will be completed, and we can recognize
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* it.
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*/
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static int pop(int fd, char *buf, size_t size, size_t npop)
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{
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ssize_t n;
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size_t len = strlen(&buf[npop]);
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memmove(buf, &buf[npop], len + 1);
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n = read(fd, &buf[len], size - len - 1);
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if (n < 0)
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return -errno;
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buf[len + n] = '\0';
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return 1;
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}
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/*
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* This will return 1, with the first character in buf being the
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* character following the next instance of c in the file. This will
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@ -61,7 +80,6 @@ static void __init find_tempdir(void)
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static int next(int fd, char *buf, size_t size, char c)
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{
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ssize_t n;
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size_t len;
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char *ptr;
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while ((ptr = strchr(buf, c)) == NULL) {
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@ -74,20 +92,129 @@ static int next(int fd, char *buf, size_t size, char c)
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buf[n] = '\0';
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}
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ptr++;
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len = strlen(ptr);
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memmove(buf, ptr, len + 1);
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return pop(fd, buf, size, ptr - buf + 1);
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}
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/*
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* Decode an octal-escaped and space-terminated path of the form used by
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* /proc/mounts. May be used to decode a path in-place. "out" must be at least
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* as large as the input. The output is always null-terminated. "len" gets the
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* length of the output, excluding the trailing null. Returns 0 if a full path
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* was successfully decoded, otherwise an error.
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*/
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static int decode_path(const char *in, char *out, size_t *len)
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{
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char *first = out;
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int c;
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int i;
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int ret = -EINVAL;
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while (1) {
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switch (*in) {
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case '\0':
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goto out;
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case ' ':
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ret = 0;
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goto out;
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case '\\':
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in++;
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c = 0;
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for (i = 0; i < 3; i++) {
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if (*in < '0' || *in > '7')
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goto out;
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c = (c << 3) | (*in++ - '0');
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}
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*(unsigned char *)out++ = (unsigned char) c;
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break;
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default:
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*out++ = *in++;
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break;
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}
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}
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out:
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*out = '\0';
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*len = out - first;
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return ret;
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}
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/*
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* Computes the length of s when encoded with three-digit octal escape sequences
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* for the characters in chars.
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*/
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static size_t octal_encoded_length(const char *s, const char *chars)
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{
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size_t len = strlen(s);
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while ((s = strpbrk(s, chars)) != NULL) {
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len += 3;
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s++;
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}
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return len;
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}
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enum {
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OUTCOME_NOTHING_MOUNTED,
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OUTCOME_TMPFS_MOUNT,
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OUTCOME_NON_TMPFS_MOUNT,
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};
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/* Read a line of /proc/mounts data looking for a tmpfs mount at "path". */
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static int read_mount(int fd, char *buf, size_t bufsize, const char *path,
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int *outcome)
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{
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int found;
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int match;
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char *space;
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size_t len;
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enum {
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MATCH_NONE,
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MATCH_EXACT,
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MATCH_PARENT,
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};
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found = next(fd, buf, bufsize, ' ');
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if (found != 1)
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return found;
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/*
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* Refill the buffer so that if there's a partial string that we care
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* about, it will be completed, and we can recognize it.
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* If there's no following space in the buffer, then this path is
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* truncated, so it can't be the one we're looking for.
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*/
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n = read(fd, &buf[len], size - len - 1);
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if (n < 0)
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return -errno;
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space = strchr(buf, ' ');
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if (space) {
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match = MATCH_NONE;
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if (!decode_path(buf, buf, &len)) {
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if (!strcmp(buf, path))
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match = MATCH_EXACT;
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else if (!strncmp(buf, path, len)
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&& (path[len] == '/' || !strcmp(buf, "/")))
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match = MATCH_PARENT;
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}
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buf[len + n] = '\0';
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return 1;
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found = pop(fd, buf, bufsize, space - buf + 1);
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if (found != 1)
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return found;
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switch (match) {
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case MATCH_EXACT:
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if (!strncmp(buf, "tmpfs", strlen("tmpfs")))
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*outcome = OUTCOME_TMPFS_MOUNT;
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else
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*outcome = OUTCOME_NON_TMPFS_MOUNT;
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break;
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case MATCH_PARENT:
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/* This mount obscures any previous ones. */
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*outcome = OUTCOME_NOTHING_MOUNTED;
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break;
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}
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}
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return next(fd, buf, bufsize, '\n');
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}
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/* which_tmpdir is called only during early boot */
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@ -106,8 +233,12 @@ static int checked_tmpdir = 0;
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*/
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static void which_tmpdir(void)
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{
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int fd, found;
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char buf[128] = { '\0' };
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int fd;
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int found;
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int outcome;
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char *path;
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char *buf;
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size_t bufsize;
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if (checked_tmpdir)
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return;
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@ -116,49 +247,66 @@ static void which_tmpdir(void)
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printf("Checking for tmpfs mount on /dev/shm...");
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path = realpath("/dev/shm", NULL);
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if (!path) {
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printf("failed to check real path, errno = %d\n", errno);
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return;
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}
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printf("%s...", path);
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/*
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* The buffer needs to be able to fit the full octal-escaped path, a
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* space, and a trailing null in order to successfully decode it.
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*/
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bufsize = octal_encoded_length(path, " \t\n\\") + 2;
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if (bufsize < 128)
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bufsize = 128;
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buf = malloc(bufsize);
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if (!buf) {
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printf("malloc failed, errno = %d\n", errno);
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goto out;
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}
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buf[0] = '\0';
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fd = open("/proc/mounts", O_RDONLY);
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if (fd < 0) {
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printf("failed to open /proc/mounts, errno = %d\n", errno);
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return;
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goto out1;
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}
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outcome = OUTCOME_NOTHING_MOUNTED;
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while (1) {
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found = next(fd, buf, ARRAY_SIZE(buf), ' ');
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if (found != 1)
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break;
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if (!strncmp(buf, "/dev/shm", strlen("/dev/shm")))
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goto found;
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found = next(fd, buf, ARRAY_SIZE(buf), '\n');
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found = read_mount(fd, buf, bufsize, path, &outcome);
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if (found != 1)
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break;
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}
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err:
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if (found == 0)
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printf("nothing mounted on /dev/shm\n");
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else if (found < 0)
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if (found < 0) {
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printf("read returned errno %d\n", -found);
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} else {
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switch (outcome) {
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case OUTCOME_TMPFS_MOUNT:
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printf("OK\n");
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default_tmpdir = "/dev/shm";
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break;
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out:
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close(fd);
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case OUTCOME_NON_TMPFS_MOUNT:
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printf("not tmpfs\n");
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break;
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return;
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found:
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found = next(fd, buf, ARRAY_SIZE(buf), ' ');
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if (found != 1)
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goto err;
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if (strncmp(buf, "tmpfs", strlen("tmpfs"))) {
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printf("not tmpfs\n");
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goto out;
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default:
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printf("nothing mounted on /dev/shm\n");
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break;
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}
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}
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printf("OK\n");
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default_tmpdir = "/dev/shm";
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goto out;
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close(fd);
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out1:
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free(buf);
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out:
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free(path);
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}
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static int __init make_tempfile(const char *template, char **out_tempname,
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