systemctl: add "systemctl cat"

3 files changed, 75 insertions, 1 deletions

diff --git a/src/shared/fileio.c b/src/shared/fileio.c
index 733b320388..ac1b409a1c 100644
--- a/src/shared/fileio.c
+++ b/src/shared/fileio.c
@@ -20,6 +20,7 @@
 ***/
 
 #include <unistd.h>
+#include <sys/sendfile.h>
 #include "fileio.h"
 #include "util.h"
 #include "strv.h"
@@ -117,6 +118,77 @@ int read_one_line_file(const char *fn, char **line) {
         return 0;
 }
 
+ssize_t sendfile_full(int out_fd, const char *fn) {
+        _cleanup_fclose_ FILE *f;
+        struct stat st;
+        int r;
+        ssize_t s;
+
+        size_t n, l;
+        _cleanup_free_ char *buf = NULL;
+
+        assert(out_fd > 0);
+        assert(fn);
+
+        f = fopen(fn, "r");
+        if (!f)
+                return -errno;
+
+        r = fstat(fileno(f), &st);
+        if (r < 0)
+                return -errno;
+
+        s = sendfile(out_fd, fileno(f), NULL, st.st_size);
+        if (s < 0)
+                if (errno == EINVAL || errno == ENOSYS) {
+                        /* continue below */
+                } else
+                        return -errno;
+        else
+                return s;
+
+        /* sendfile() failed, fall back to read/write */
+
+        /* Safety check */
+        if (st.st_size > 4*1024*1024)
+                return -E2BIG;
+
+        n = st.st_size > 0 ? st.st_size : LINE_MAX;
+        l = 0;
+
+        while (true) {
+                char *t;
+                size_t k;
+
+                t = realloc(buf, n);
+                if (!t)
+                        return -ENOMEM;
+
+                buf = t;
+                k = fread(buf + l, 1, n - l, f);
+
+                if (k <= 0) {
+                        if (ferror(f))
+                                return -errno;
+
+                        break;
+                }
+
+                l += k;
+                n *= 2;
+
+                /* Safety check */
+                if (n > 4*1024*1024)
+                        return -E2BIG;
+        }
+
+        r = write(out_fd, buf, l);
+        if (r < 0)
+                return -errno;
+
+        return (ssize_t) l;
+}
+
 int read_full_file(const char *fn, char **contents, size_t *size) {
         _cleanup_fclose_ FILE *f = NULL;
         size_t n, l;
@@ -168,7 +240,6 @@ int read_full_file(const char *fn, char **contents, size_t *size) {
 
         buf[l] = 0;
         *contents = buf;
-        buf = NULL;
 
         if (size)
                 *size = l;
diff --git a/src/shared/fileio.h b/src/shared/fileio.h
index 59e41502b1..06c2887157 100644
--- a/src/shared/fileio.h
+++ b/src/shared/fileio.h
@@ -31,6 +31,7 @@ int write_string_file_atomic(const char *fn, const char *line);
 
 int read_one_line_file(const char *fn, char **line);
 int read_full_file(const char *fn, char **contents, size_t *size);
+ssize_t sendfile_full(int out_fd, const char *fn);
 
 int parse_env_file(const char *fname, const char *separator, ...) _sentinel_;
 int load_env_file(const char *fname, const char *separator, char ***l);
diff --git a/src/shared/util.c b/src/shared/util.c
index 206fc803d0..305a6c2fb6 100644
--- a/src/shared/util.c
+++ b/src/shared/util.c
@@ -5791,6 +5791,8 @@ void* greedy_realloc(void **p, size_t *allocated, size_t need) {
         size_t a;
         void *q;
 
+        assert(allocated);
+
         if (*allocated >= need)
                 return *p;