From e789d236a3fcc7c26c8c7c5376f5b7beb6fabcf7 Mon Sep 17 00:00:00 2001 From: Paul Eggert Date: Sat, 12 Jul 2025 10:03:26 -0700 Subject: [PATCH] Improve inserted file coding system finding MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit * src/fileio.c (Finsert_file_contents): When inserting a file into a nonempty buffer, improve the heuristic for determining the file’s coding system by not trusting lseek+SEEK_END, which is unreliable in /proc or when the file is mutating. (cherry picked from commit 6a9dbed40ccebc18fda6078058b1978e29ef98fa) --- src/fileio.c | 36 +++++++++++++++++++++++++++++++----- 1 file changed, 31 insertions(+), 5 deletions(-) diff --git a/src/fileio.c b/src/fileio.c index cbdfeacf8e4..5d383a7b44d 100644 --- a/src/fileio.c +++ b/src/fileio.c @@ -4289,12 +4289,38 @@ by calling `format-decode', which see. */) { off_t tailoff = emacs_fd_lseek (fd, - 3 * 1024, SEEK_END); if (tailoff < 0) - seekable = false; - else if (1024 < tailoff) { - ptrdiff_t ntail = emacs_fd_read (fd, read_buf + 1024, - 3 * 1024); - nread = ntail < 0 ? ntail : 1024 + ntail; + seekable = false; + tailoff = nread; + } + + /* When appending the last 3 KiB, read until EOF + without trusting tailoff, as the file may be in + /proc or be mutating. */ + nread = 1024; + for (;;) + { + ptrdiff_t r = emacs_fd_read (fd, read_buf + nread, + sizeof read_buf - nread); + if (r <= 0) + { + if (r < 0) + nread = r; + else + file_size_hint = tailoff; + break; + } + tailoff += r; + nread += r; + bool eof = nread < sizeof read_buf; + if (4 * 1024 < nread) + { + memmove (read_buf + 1024, + read_buf + nread - 3 * 1024, 3 * 1024); + nread = 4 * 1024; + } + if (eof) + break; } } -- 2.39.5