fileio: make sure read_full_stream() works on memory-backed streams

diff --git a/src/basic/fileio.c b/src/basic/fileio.c
index 8b744c11ea3669e197dcd1bf4d59a753c2df38ff..859298ff02fa3df85edeff84dd7e0d00589fdaee 100644 (file)
--- a/src/basic/fileio.c
+++ b/src/basic/fileio.c
@@ -263,29 +263,35 @@ int verify_file(const char *fn, const char *blob, bool accept_extra_nl) {
 }
 
 int read_full_stream(FILE *f, char **contents, size_t *size) {
-        size_t n, l;
         _cleanup_free_ char *buf = NULL;
         struct stat st;
+        size_t n, l;
+        int fd;
 
         assert(f);
         assert(contents);
 
-        if (fstat(fileno(f), &st) < 0)
-                return -errno;
-
         n = LINE_MAX;
 
-        if (S_ISREG(st.st_mode)) {
+        fd = fileno(f);
+        if (fd >= 0) { /* If the FILE* object is backed by an fd (as opposed to memory or such, see fmemopen(), let's
+                        * optimize our buffering) */
 
-                /* Safety check */
-                if (st.st_size > READ_FULL_BYTES_MAX)
-                        return -E2BIG;
+                if (fstat(fileno(f), &st) < 0)
+                        return -errno;
+
+                if (S_ISREG(st.st_mode)) {
 
-                /* Start with the right file size, but be prepared for files from /proc which generally report a file
-                 * size of 0. Note that we increase the size to read here by one, so that the first read attempt
-                 * already makes us notice the EOF. */
-                if (st.st_size > 0)
-                        n = st.st_size + 1;
+                        /* Safety check */
+                        if (st.st_size > READ_FULL_BYTES_MAX)
+                                return -E2BIG;
+
+                        /* Start with the right file size, but be prepared for files from /proc which generally report a file
+                         * size of 0. Note that we increase the size to read here by one, so that the first read attempt
+                         * already makes us notice the EOF. */
+                        if (st.st_size > 0)
+                                n = st.st_size + 1;
+                }
         }
 
         l = 0;